I really think a skip to 1st grade is inconsequential. At least where I live, not much is done in kindergarten. Even though my son (who is 5) was able to do 2nd & 3rd grade stuff, a single grade skip has been terrific because he's developing nice handwriting, meeting older kids (he's a very young 5, there's an 8 yr old in his class), and learning quite a bit (surprisingly)--nouns, verbs, adjectives, synonyms, homonyms, antonyms, punctuation, etc.
Maybe see if both twins could skip, even without the documentation for your daughter. Sometimes the Iowa Acceleration Scale and in-school testing (STAR math & early literacy benchmarks) may be adequate to demonstrate mastery. Spend second semester in 1st grade and it gives you half a year to figure out what more to do.
My son spent 1st semester in 1st grade without an IEP in place (thanks to a brave principal) and even though he's the very youngest in the class, he's the top performer. In January, we switch him to a self-contained gifted class with 5 kids in K-2. My heart breaks because he's really enjoyed his 1st grade class, but I keep telling myself that it's better to give him opportunities to progress (the 1st grade math curriculum is stuff he was doing 2 yrs ago and in the new class he will be able to work at a more challenging level). I also didn't like that everyone in the class would tell him (and me, when I visited) how smart he was. "He's so smart--he's the smartest one in our class", over and over, and then I'd hear him reiterate it (yuck). I hope that having him in a class of his "peers" he'll understand that there are other smart kids out there and not to make a big deal of it, but to make something of it.
