@typiCAmom,
I would not recommend taking a cc chemistry course over the summer just to avoid hs chemistry. If you expect her to complete BC calc in hs then clearly she has no particular difficulty with STEM and she will likely find hs chemistry to be no problem. A lot of the early material is just basic algebra, so many unit conversion problems.
She does not have to do SAT prep during her sophomore year. I wouldn’t recommend that unless she really has the time and expects to be very busy over the summer. I’d suggest to focus on school and ECs. She can do SAT prep over the summer–if she isn’t taking a chemistry course she doesn’t want to be taking at the cc.