There have never been any confirmed cases of HepB being transmitted via oral sex: https://www.hepb.org/blog/much-really-know-sex-hepatitis-b-take-quiz-find/
That doesn't mean the risk doesn't exist. It's up to her to decide whether the risk is negligible enough. Another option is for her to have her titers checked, to see if she is already immune to HepB via vaccination.