(Wanting something someone else has, not the relationship jealous.)

I've been struggling to forgive a mutual "friend" who is the ex of my mate's buddy. Though they broke up, she visited us a few times and on at least one of those occasions, she stole an object of sentimental value. The object is an item that my mate and I kept because it reminded us of when we met. There would normally be no value to anyone else. After some pressure and evidence, she did admit to taking it, but would never admit to why. I don't think we'll be seeing her for a long time. (No, we do not have the object back.)

It has become obvious to us that she was jealous of our relationship. I am furious because I valued the object, I trusted her, and I feel like a fool that it happened, even though I/we really did nothing wrong. In order to get past this--it happened many months ago--I think I just need to forgive her. I can't seem to stop thinking about the fact that someone would steal a useless object just because they're jealous. I just don't understand it. Because she didn't talk about why she did it, I feel this missing link to resolving the incident.

This is an awkward question, but maybe someone can say the right thing to help. If you have ever been jealous in this or a similar way, please write to explain the impulse to do harm. What must our friend be feeling? Is it appropriate for me to ban her from our house? Talking about your own "incident" may help you too.