Is a girl who continued masturbating in Ramadan, with doubt about ejaculation and not remembering when she learned that ejaculation invalidates the fast, required to make up the days and offer expiation?

You must repent to Allah with sincere repentance and not return to the sinful act. Your fast is not invalidated by this, as long as you were ignorant that it breaks the fast, whether semen was emitted from you or not. Therefore, you are not required to make up the fast nor offer expiation.