No experience with BYU, but we've had good experiences with online college courses at the local community college--which, in our state, are also fairly inexpensive, due to state early college/dual enrollment initiatives ($200/course, plus or minus). Check your local CC. In some states, a limited number of courses can be taken for free as dual enrollment (funding permitting and space available). It won't be self-paced, most likely, but there will probably be more options for course selection, and possibly some transferability for HS credit, depending on your state regs. She'll probably have to submit some documentation from her school, and take placement exams. It's usually a minimum of hassle.
Some info on dual/concurrent info in NE states:
https://nebhe.org/info/pdf/policy/Policy_Spotlight_Dual_Enrollment_in_New_England.pdf
