One of the old story models is the lesbian "turned' straight because of the rapist's prowess. It's a bit far-fetched, but this is a fantasy world after all. Kind of a variation on the old non-consent story where the rape victim is then the "reluctant" victim, finding she is being aroused and climaxed because of (again) the "rapist's sexual prowess."

A plot worth exploring would be where the straight victim is re-oriented to a lesbian identity/orientation. This might be more feasible in real-life. A hetero victim of rape, now disaffected by men, gets introduced to the rape-crisis network which is (actually) heavily populated by femininists and lesbians.

Then she gets introduced to lesbianism.

Now there's a scenario for ya!