She also, with a few brief lapses, doesn't think she *NEEDS* to be in a relationship. It's been this big huge stretch for her to get and be in a relationship at all, and if it gets substantially less convenient to maintain, like she is getting beat on, she can go back to being single. She's been alone and relatively content for a long time -- which I think would help her say "fuck off, evil abusive bastard" without being OMG SO AFEARED of being left alone.

Emotional manipulation is less obvious. While Sam totally KICKS ASS in a lot of ways, I suspect she's pretty insecure socially... so if someone she cares about tells her things that boil down to "this is wrong because YOU are not doing enough," I think that would be a sucker-punch right to her weak spot. I also don't think she's been in enough (if any) really GOOD, healthy relationships to have a clear picture that This Is Not The Way It Should Be.