I don’t think a B+ in one subject is going to tank anyone’s application. My advice would be to figure out what your daughter is looking for in a school and then find schools that offer those things and feel like a good “social” fit for her. My daughter was looking for a “kind community” of students and teachers, a smaller size (about 300-400 kids), a theater program, a XC team, and a healthy academic/life balance (so no “grind” schools for her). That helped us get started and then visits, virtual panels (we are not close enough to attend in-person events regularly), and more research/thinking allowed her to figure out what was important and what she could live with (or live without). In the end, she applied to six schools this year as an 8th grader. None of which would be considered in the “top tier”, but all of which fit each of her criteria and she would be delighted to attend any of them.
In terms of schools in NY or CT, my daughter applied to Emma Willard, Millbrook, Suffield, Pomfret, and Miss Porter’s from those two states.