The "I must have done something to deserve my abuse" is very, very common among survivors of child abuse. It's the way the brain, especially the immature brain of a child, copes with unbearable behavior from someone who should be protecting the child.
It's not something you can talk a person out of. There are techniques (I'd like to second the recommendation for The Body Keeps the Score), but talk therapy is not all that effective at dealing with trauma, especially childhood trauma. Unfortunately, the psychiatric establishment doesn't yet believe in childhood trauma (heck, a lot of them don't even believe in DID) which is why it isn't in the DSM V.
(Of course, the psychiatric establishment didn't believe incest existed, either, until incest survivors groups browbeat them into grudgingly accepting it. Same for PTSD. Etc., etc.)