I’ve heard of the following American seminaries:
1-Montreal (very academic)
2-Toronto (has a six week trip to Eretz Yisrael after Pesach)
3-Machon Basya Rochel (Rebbetzin Feiner’s seminary in the Five Towns, very warm, not so academic)
4-Bais Yaakov Intesive
5-Bais Yaakov Half Day
6-Machon
7-BYA
8-The NY Sem=V’At Alit (Rebbetzin Asaf’s seminary, very academic, full day program I think)
9-Bnos Chaim (Lakewood)
10-The Lakewood Seminary (separate from Bnos Chaim, but I don’t remember its real name)
11-Maalot Baltimore (has a trip to Eretz Yisrael January time)
12-Yavne in Cleveland (very academic, small, might not be around for much longer)
There used to be another seminary in Detroit but it closed down a couple of years ago.
As you can see, there are plenty of options for girls wanting to stay in America. However, I don’t know very much about the seminaries on my list. I’ve merely heard of most of them. Some have dorms, some don’t. Some have options for boarding by local families (ex-Yavne). Some are more academic than others. I suggest you take this list as a starting point and narrow it down from there. If I remember any other American seminaries I’ll try to post them. Hatzalachah Rabba with your search!