Well, according to local Head Watcher Lady Terry, they kind of were taking advantage of her/had her brainwashed. That's the story. She's not a BAD person, she's just...painfully screwed up. Still, that's not an excuse. We all got issues.

(...How horrible is it of me that sometimes I think, 'Thank God they all died except Giles?' The more I hear about them, the more I think it.)