You can have some power over how you feel, but it’s not OK for her to be like, “Well, if you’re jealous that’s your problem. Sort it out.” Especially because you didn’t negotiate an open relationship, and she’s only recently admitted what’s really going on. Now that it’s out in the open, you need to talk about how you’re going to deal with this, and find a compromise.

Have you read any of the material on polyamory? “The Ethical Slut” is a classic but there’s other books and information online. Some polyamorists are superior knobheads, but if you can find your way around them you can find some really good stuff about dealing with jealousy, and how your partner can help you work with it. Even if you don’t feel an open relationship is what you want, it’s useful stuff. Polyamorist know their stuff when it comes to jealousy. They deal with it a lot. :/

She should give your feelings more consideration than she seems to be doing at the moment.

I don’t think it’s that useful getting too involved with how the other couple is handling this. I mean, be friendly if you can, but their relationship is their business, you know? Don’t play tactics or “call her bluff”. You’re not in high school.