Welcome Nicky! You've gotten some great advice from others already. I thought I'd just pop in with my 2 cents.
I recommend finding any policies on Gifted for your state (state Dept. of Education website) and for your district. There may be some sort of outline already there for how schools are supposed to deal with gifties.
Think about possibly meeting with the principal and teacher ahead of time to discuss your concerns. Tell them you are worried that your DD already knows much of the kindy curriculum, mention what she can do. Ask them what sorts of policies/procedures they have for acceleration or grouping or differentiation. (E.g., do they test in the beginning of the year and group kids with similar abilities? Is there any chance of moving up to 1st for certain subjects?) Think about what your goals are for kindergarten for your DD. Has she had a lot of experience in settings with other kids, or will kindergarten be her first experience in how to "do school"? There are a lot of lines, getting ready on your own, dealing with dynamics of a full class of kids that is also learning. It sounds like your DD can already read and write pretty well... for our son, he refused to learn to write before school, so at least we had that goal for kindy.
Think about the possibility of full grade acceleration and the pros and cons.
Think about whether homeschooling is an option. It's a great stress reliever if you start school with a backup plan.
I would check with the school to see if they could test your DD. My son's school did achievement testing before kindy. We chose to get him privately tested at 4, thinking about a possible early entrance. The test scores came in handy in convincing the school we were not just making things up. For us, the report that came with the test, explaining what the scores meant, was the best part. We used a tester familiar with GT kids. But I wouldn't recommend paying for it unless you have a goal in mind that requires you having the scores.
In my opinion, most GT parents will have GT kids.
