K.C.
It's up to you. My son will be 6 in June, and he won't start Kindergarten until this fall. I was going to put him in this last year, but he was going to be overloaded to a different school farther away- so the principal recommended that I wait another year to enroll him.
I'm actually kind of glad now- because he's small for his age...
If you feel she's ready to go- go ahead and put her in. Either way it's up to you.