I would have written: She's nervous about performing...
or (with a different meaning) : She's too nervous to perform

Another example of where phrase/context/meaning may be at odds is "How are you?". This is often more politeness rather than a real enquiry. Answering with anything other than "fine" or "good" may not be what is sought.

Likewise, the waitress, the receptionist, the yoga teacher may greet you with a "friendly" intonation, and a smile. It does not mean they would welcome a date. In fact their real attitude beneath the "professional" overly may be hard to determine.

Intonation conveys attitude, part of the meta-data of speech; but it is more difficult to research; and hard to teach to English learners whose native intontion patterns may be quite different. Try watching Vladimir Putin, or Ban Ki Moon; the smile/non-smile and intonations convey perhaps the wrong message to native English speakers

One way of looking at English is to view it as a collection of patterns, collocations, phrases and idioms, from which if needed we may identify some 'rules'. However there is also the matter of register, date, context, genre, intonation, background culture and which dialect of English we are addressing. All these things influence the actual meaning conveyed, and undermine the idea that there are all-time all-encompassing rules, or 'right' or 'wrong' English.

Teaching English as a second (or third) language is a somewhat special case, which is dominated by the required end-use: English for business purposes focuses on business phrases, situations and vocabulary, and pays scant attention to slang, general idioms, and informal items which are not important. One cannot hope to cover everything. It is enough to be clear, use appropriate intonation, register and style, and know enough about the culture not to put your foot in it.

That said, the real message contained in an utterance may be quite at odds with the actual word forms: consider for instance how many ways one can say "Really" in various contexts. It may convey surprise, indicate interest, or (with a flat or falling intonation) suggest disinterest. In the same way "Give me a call sometime" might indicate real interest or almost quite the opposite, depending on context. So focussing entirely on the words is by no means the whole story, although in teaching English one must start somewhere.

Ah I meant before 1840.

http://books.google.com/ngrams/graph?content=she+arrives+tomorrow%2Che+arrives+tomorrow%2Cthey+arrive+tomorrow&case_insensitive=on&year_start=1500&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t4%3B%2Cshe%20arrives%20tomorrow%3B%2Cc0%3B%2Cs0%3B%3Bshe%20arrives%20tomorrow%3B%2Cc0%3B%3BShe%20arrives%20tomorrow%3B%2Cc0%3B.t4%3B%2Che%20arrives%20tomorrow%3B%2Cc0%3B%2Cs0%3B%3Bhe%20arrives%20tomorrow%3B%2Cc0%3B%3BHe%20arrives%20tomorrow%3B%2Cc0%3B.t4%3B%2Cthey%20arrive%20tomorrow%3B%2Cc0%3B%2Cs0%3B%3Bthey%20arrive%20tomorrow%3B%2Cc0%3B%3BThey%20arrive%20tomorrow%3B%2Cc0

http://books.google.com/ngrams/graph?content=she+comes+tomorrow%2Che+comes+tomorrow%2Cthey+come+tomorrow%2Che+comes+on+the+morrow&case_insensitive=on&year_start=1500&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cshe%20comes%20tomorrow%3B%2Cc0%3B.t4%3B%2Che%20comes%20tomorrow%3B%2Cc0%3B%2Cs0%3B%3Bhe%20comes%20tomorrow%3B%2Cc0%3B%3BHe%20comes%20tomorrow%3B%2Cc0%3B.t4%3B%2Cthey%20come%20tomorrow%3B%2Cc0%3B%2Cs0%3B%3Bthey%20come%20tomorrow%3B%2Cc0%3B%3BThey%20come%20tomorrow%3B%2Cc0

http://books.google.com/ngrams/graph?content=she+comes+in+the+morning%2C+he+comes+in+the+morning&case_insensitive=on&year_start=1500&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t4%3B%2Cshe%20comes%20in%20the%20morning%3B%2Cc0%3B%2Cs0%3B%3Bshe%20comes%20in%20the%20morning%3B%2Cc0%3B%3BShe%20comes%20in%20the%20morning%3B%2Cc0%3B.t4%3B%2Che%20comes%20in%20the%20morning%3B%2Cc0%3B%2Cs0%3B%3Bhe%20comes%20in%20the%20morning%3B%2Cc0%3B%3BHe%20comes%20in%20the%20morning%3B%2Cc0

I thought using present simple when referrring to the future was a hang-over from OE; but here it looks as though it only began with the coming of railways and timetables. One needs however to be mindful that "tomorrow" was more oft spelt "to-morrow" before 1930.

So the question is how did they say "She/He/They is/are coming tomorrow" before 1850?
Or did they never say it?
I get no results

@WW thank you; most interesting.

I am not sure how representative the verb "come" is. Here are some others that show contrary patterns of usage:

http://books.google.com/ngrams/graph?content=wiil+stay%2Cstays%2Cis+staying%2Care+staying&year_start=1500&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cstays%3B%2Cc0%3B.t1%3B%2Cis%20staying%3B%2Cc0%3B.t1%3B%2Care%20staying%3B%2Cc0

http://books.google.com/ngrams/graph?content=arrives%2Cis+arriving%2Care+arriving&year_start=1500&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Carrives%3B%2Cc0%3B.t1%3B%2Cis%20arriving%3B%2Cc0%3B.t1%3B%2Care%20arriving%3B%2Cc0

http://books.google.com/ngrams/graph?content=is+wanting%2Care+wanting%2Chas+been+wanting%2Chave+been+wanting&year_start=1500&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cis%20wanting%3B%2Cc0%3B.t1%3B%2Care%20wanting%3B%2Cc0%3B.t1%3B%2Chas%20been%20wanting%3B%2Cc0%3B.t1%3B%2Chave%20been%20wanting%3B%2Cc0

I can't quite believe that the growht in the incidence of present continuous was due to some spin-off from teaching English in Welsh schools after 1847. Would be nice to pin it all on the evil influence of Latinate grammarians, but that doubtless wouldn't stack up either.

It does seem though that modern English usage of present continuous (a la Murphy) is very much a 20th century thing, and that in the Victorian Era usage was either less consistent or just slightly different

Just trying to get a handle on when present continuous became so widespread in English and began to be used instead of will/shall

Taking "comes" vs "is coming" as an example, and beginning with Chaucer, I have not so far found instances of present continuous. Looking at another source:

http://en.wikipedia.org/wiki/Sumer_Is_Icumen_In

the present continuous is again not used.

Again looking at the KJV (which sometimes reflects older usage from Tyndall's), we find present simple: ()not the night is coming)
John 9:4:
I must work the works of him that sent me, while it is day: the night cometh, when no man can work.
Similarly Revelation 1:7
OTOH "is coming" is found in Pilgrims's Progress and later in Pride and Prejudice

So the question remains: was present continuous somehow not as common at the beginning of the Victorian Era as toward the end? Or was the changeover complete before Vikki got on the throne?

OOPS meant to post:

http://books.google.com/ngrams/graph?content=she+has+issues%2C+he+has+issues%2C+you+have+issues&case_insensitive=on&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t4%3B%2Cshe%20has%20issues%3B%2Cc0%3B%2Cs0%3B%3Bshe%20has%20issues%3B%2Cc0%3B%3BShe%20has%20issues%3B%2Cc0%3B.t4%3B%2Che%20has%20issues%3B%2Cc0%3B%2Cs0%3B%3Bhe%20has%20issues%3B%2Cc0%3B%3BHe%20has%20issues%3B%2Cc0%3B.t4%3B%2Cyou%20have%20issues%3B%2Cc0%3B%2Cs0%3B%3Byou%20have%20issues%3B%2Cc0%3B%3BYou%20have%20issues%3B%2Cc0

@DN Do you have some kind of an issue with that??

http://books.google.com/ngrams/graph?content=problem%3Aeng_us_2012%2Cissue%3Aeng_us_2012.%2Cproblem%3Aeng_gb_2012%2Cissue%3Aeng_gb_2012&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cproblem%3Aeng_us_2012%3B%2Cc0%3B.t1%3B%2Cissue%3Aeng_us_2012.%3B%2Cc0%3B.t1%3B%2Cproblem%3Aeng_gb_2012%3B%2Cc0%3B.t1%3B%2Cissue%3Aeng_gb_2012%3B%2Cc0

@DN Do you have some kind of an issue with that??

http://books.google.com/ngrams/graph?content=is+coming%2Cwill+come%2Cwill+be+coming%2Care+coming%2Cshall+come&year_start=1500&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cis%20coming%3B%2Cc0%3B.t1%3B%2Cwill%20come%3B%2Cc0%3B.t1%3B%2Cwill%20be%20coming%3B%2Cc0%3B.t1%3B%2Care%20coming%3B%2Cc0%3B.t1%3B%2Cshall%20come%3B%2Cc0

Short though she was, Victoria ascented the throne in 1837; so at the start of the Vicotorian Era "shall" may have been used as oft as will.

Present continuous seems to have grown during her long regnum.

You are right about 'here comes' ; what I meant to imply was that putting the adverb of place first will allow the use of a simple verb instead of continuous without breaking modern verb patterns : eg Into the station pulled the train. Whether this is a good idea or not hinges on the context of course.

You might wish to review my late ramblngs on the Anglish thread; I was much surprised at how seldom future continuous crops up, and the fact that "have been wanting" was relatively common a few hundred years ago. Not quite sure that Headway etc get the right emphasis on what matters.