Is the montissori a mixed age classroom setting? If she is gravitating to the older kid's work, to the older kid's in general, and her teachers are recommending it, I would probably do it.
However, are you moving to public school for certain after K then? You might already want to be looking to see if your public school is going to allow her to move right to 1st grade and what possible accommodations might be. Since you have an older child, maybe you already have a good feel for how/if it is going to work. Good luck! I'm sure it will be great whatever you decide.
