It's just hard work for a 6yo to function socially in such a big classroom.
Just to shed a ray of hope... prior to recent decades' focus on smaller class size, I'm familiar with class sizes up to 60 kids, operating successfully. Just as there are more factors to individual success than IQ (which is frequently the subject of focus)... there are more factors to classroom success than class size (which is frequently the subject of focus).
There is good and bad in everything. In some ways, a larger number of kids in a classroom can be a benefit socially as it provides more options for finding kids with whom a child has interests in common... potential friends and groups of friends.
That said, it's good for kids to be aware of their surroundings and whether there seems to be a positive energy or a negative vibe. Without frightening kiddo, as a part of personal safety, I'd encourage kiddo to be observant of her environments as she goes about her daily routine... including being observant in the classroom. For the learning environment I'd caution kiddo to be watchful for anything which might seem to have the potential to lead to trouble... such as materials being out-of-reach, or a child who may take most of the teacher's attention, may not listen or may misbehave, play tricks on others, try to get other kids to misbehave, boast of lying, of getting away with things and not getting caught, sneaking out of class, or other safety issues which may be related to classroom management and the student:teacher ratio.
Having a dinner time routine of family members sharing and talking about their day can be helpful... for example: sharing a good thing... a bad thing... something you'd like to change or wish was different. If kids are used talking about their day, these casual conversations can provide a great early-warning system to parents.
