In my daughters school, the girls are not allowed to have a Bat Mitzvah party(birthday parties are not allowed either). They tell the parents that it is a special time to be shared with the girl’s family only.
Another girls yeshiva nearby also, banned the Bat Mitzvah parties. Some of the wealthier families were just making really big parties and it was getting out of hand.
A realitive of mine made her daughter a bat mitzvah party at home. She made a Meleve Malka and as an activity, for the girls, she bought a paint by number kit, which she found very cheap. They played music and danced after. Very nice and very simple.