I say, go ahead and put her in. The cut off is silly, especially if you only miss it by a few weeks. In several other states (ie California) children are enrolled in school based on the calendar year NOT some silly academic year. For instance, all children born in 2005 will enter Kindergarten in the fall of 2010.
I disagree that Kindergarten is "a lot different than preschool." I have a preschooler and a kindergartener right now. Guess what? They are learning the exact same things. Kindergarten is technically optional in the state of Utah anyway.
Also, with the whole "no child left behind" plan, the curriculum in all of the grades has been geared way back. We used to learn multiplication and cursive at the beginning of 2nd grade. Now, children do not learn either of those concepts until 3rd grade.
Listen, we are struggling with one possible outcome of this problem here. Our son has an October birthday. At the time we wanted to have him go to Kindergarten he obviously "missed the deadline." We didn't know all of the other options (like private Kindergarten, etc) so he ended up suffering with boredom through 3 years of school. Yes, you can do extra homework projects with them, but when they have to sit and right letters and words over and over again in Kindergarten, 1st, and 2nd grade (the "boring & tedious" homework) they are in no mood to do your extra "stimulating" homework. They are practically bleary eyed from the tedious stuff that gets sent home already.
This year, we ended up skipping him a grade. He went from 2nd grade to 4th grade. THAT has been a challenge. It is much harder to have to do it later on. Third grade is not a grade I would recommend skipping.
My guess is that if your child has even average intelligence (and she sounds like she is actually above average) she can definitely handle kindergarten next year.
It is much harder to have to skip her later on. If you do end up waiting and down the line you end up skipping, I would recommend skipping 2nd grade. It is the most useless grade--It is basically a repeat of Kindergarten and 1st. We have been through 2nd grade with two of our kids already (within the last 3 years) and both of them nearly died from boredom.
Good luck with your choice. The most important thing to remember is this: While we clearly all have an opinion on this subject, it ultimately is YOUR choice. If you decide to wait, great. If you decide to put her in, that is great, too. YOU know what is best for your child. Don't let anybody make you feel bad about the decision that you make because they cannot possibly know your child as well as you do.