GHS,
Your DD is doing K in the same montessori and the school initiate the plan instead of you pushing it which means that your DD is ready.
My DD was in the same boat. My DD was 4 when she was in K and they did 1st grade the next year for her. She was the only 1st grader in her class with the rest are pre K and a few K. We had doubt about how it could work. The teacher was very good at differentiation and my DD was happy at school. She even acted as teacher assistant (she likes being in charge) and read some stories, taught them puzzle, etc...and it was a good experience for her.
