If guilty, I don't think it'll be any reason that's comprehensible to most of us - in my opinion there has to be something not right mentally to cause it. We've all observed her thought patterns don't make sense in some ways; weird answers in cross examination when even us lay people can come up with better explanations/excuses, seemingly compulsive hoarding/acquisitions of papers she shouldn't be keeping, the bizzarre self-contradictory notes she's written, a general sense of her appearing to think she's superior to others, etc etc.
I don't know what that all adds up to, but there's something weird about her thought processes, and I think it's likely that, if guilty, her reasons for what she's accused of will make as little sense as the other things already much discussed. If even she knows why she's done them (if guilty) - it may well be that she doesn't know either.
I'm expecting many documentaries with psychologists and criminologists trying to explain her, if she's found guilty, and probably none of them will come up with anything more indepth than we already have here! I hope I'm wrong though, as if she's guilty, I'd really like to know what led up to it, as it seems so inexplicable at present.