To be blunt, I think the serious trouble in your social group is going to happen at some point. With a "friend" like this, I'm anticipating that she'll do something, at some point in time, to someone and then all heck will break loose.
OP, you know your friends better than I do. But I would be seriously upset with a friend who knew about the violation of my personal space and didn't tell me.
I know you are trying to to the right thing, and I know it isn't going to be easy to have any kind of conversation about this "friend." But I think it is hard to provide evidence for something as vague as "she doesn't support your relationship," and a lot easier to prove that Jenny shouldn't let this "friend" into her home again.
I have been thinking more about what I'd specifically say. Honestly I don't think I would actually say "she doesn't support your relationship
" because I don't think I could pull it off and Jenny would likely burst out laughing. I'd probably just bring it up along the lines of:
"Hey I want to talk to you about something. I consider both you and Todd my friends, and I think that you should know about this, I don't want you to get blindsided and I just want to drop you a warning. You know how Friend gets really negative/obsessed about certain things, like her and "The Troll?" (Jenny will know what that means
) I know gossip isn't exactly unusual around here, but over last semester, I was noticing things that she was saying about you and Todd that I know I would want someone to tell me. It's gotten to the point that pretty much any time she notices anything that you guys do as a couple, whether it's just doing something sweet for each other or sharing dessert, etc., it gets retold with x10 snarkiness. But it isn't limited to her saying it here, she has been doing it with her friends from XUniversity, like how she got with the "Practically Perfect" thing (and wow I just realized how many of these "things" Friend has...
). It may not be a big deal to you, but I wanted to tell you so that at least you are forewarned that what you say to her, doesn't stay with her."
Ok that was a general idea of what I was thinking. Though now that I think about the situations that I was alluding to, I'm wondering if the picture issue would even make things worse or if it is just more of the same thing. Alright, I have a feeling that when it comes down to it, I'm going to tell her about it. I hate hiding things, especially something like this. So maybe I'd follow up with a "There's once incident in particular that I need to tell you about..."
ETA: I am realizing that most of my discomfort with this situation stems from the fact that I don't feel comfortable presenting myself as Jenny's friend while keeping something that is hurtful to her to myself - that's not being a real friend. I'm going to have to share that part. If other people get upset, well, at least I know I'll have a less murky conscience.