If they haven't been invited in the past, and she is your peer, she was wrong to do so without asking the group. On the other hand, you can't really uninvite them without being rude. The options you have are to attend or not. If you attend, you need to bring a dish, maybe not as nice as you were planning, but still bring one, and then you can leave relatively soon, making an excuse such as not feeling well or a press or work to attend to. If you don't attend, then you should make an excuse ahead of time, like a dental appointment or something along those lines.
I think you'd do better to attend and use this as an opportunity to try to resolve some of the issues you have encountered or at least build some bridges.