Nightstalker, I agreed with pretty much everything you said in your post. It's seldom the case that I read a post and think that. I didn't notice if anyone else commented on it or not. You seem to think things through despite the fact that your nickname creeps me out.
As far as the reason of why Kelly Lynch would mess Leonard over, there could be many. It could be the jilted lover thing as Lizzy mentioned but I'd say that it has more to do with that most American idea of greed and the hustler/gangster mentality that is at the heart of capitialism. Actually, it was probably a combination of things...as situations often are.
Geoffery, if this is all a devine event inspired by the creator so that you can see Leonard in concert, and that Mrs. Lynch is bandaging up stigmata as I write this, I would have to say that she's going to be getting the Christ tratment (figuratively, at least) pretty soon.
I don't give it religious overtones though. It was just one person screwing over another person royally. It happens every day in a variety of ways. Some people get caught and lots of them don't.
When you guys were coming up with all of these reasons of why she might have stolen from him, I'll just go the simple route and not try to justify it with anything. Some people are honest and some people aren't. As strange as it seems, it does boil down to that. All of the justifying makes me think of an old friend who was cheating on their spouse and gave me about ten reasons why it was okay to do so...I just said that you don't have to get permission from me, you were the one who made promises and took vows, and not to me. What you're trying to do is give permission to yourself. I think the point was taken and it wasn't mentioned again.
I'm not trying to moralize other than to say, take responsibility and don't make excuses. I've made my mistakes too. They just didn't happen to involve 5 million dollars of someone else's money.

That was all more than I was intending to write.
Kevin