I'm not sure from your post what the teachers mean by "immaturity?" Did they give you examples? Maybe they have some valid concerns?

I wonder is her behavior better in K, or in groups with 1st or 2nd graders?

I see no issue with her running around with the boys-- I don't see that as immature, maybe she'd prefer to do that than the things the girls are doing?

I know I only posted questions and not answers, but I hope that thinking about those may help.