Chris- I'm going to say hard stuff- make sure you've had coffee. :-)
I would not ever want a child to be put in a spot where the mid-year drop back was an actual possibility. I think it often makes the school feel more comfortable to say it's a "trial" period. IMHO, that option is there as a "do not sue us" coverage, but shouldn't be there with any time the parent isn't too confident of the skip. I believe it would feel like the child had failed to meet everyone's expectations and that she wasn't "as smart" as you thought she was.
My son skipped mid year and still, two years later, his biggest fear is that he is an imposter and someone will find out. He was strongly prepared, skipped up at the top of the next grade and made friends easily. But if he got in the slightest bit of trouble last year, missed a math problem, didn't write his "best" on a paper, his first reaction was always "please, please don't make me go back, I'm sorry!"
If you think she's ready to do 1st, I see no reason not to try! I would say however, that it might be better to have her redo 1st again next year, rather than return to K, if you find out it's not working. Or consider doing 1st again somewhere else if she needs to catch up. But a mid-year downgrade to K seems harsh and punishing, particularly for girls. I don't know why but 1st grade girls have a twinge of middle-school girl in them. While I haven't done it myself, I imagine the playground teasing would be relentless.
On a related note, my son went from barely reading BOB books to reading 3rd grade chapter books within 4 weeks of getting his glasses :-)
