Not sure I have a lot of good advice, but didn't want to leave this unanswered. It's really hard. Some thoughts below, please ignore any that aren't helpful.
Is she sure this new exclusion is actually deliberate and a reflection of how her friendship group see her, rather than a misunderstanding/misperception? (Not saying it isn't, obviously I have no idea.) I do know from watching the teenagers around me (I have 3, so see a lot of them) that most of them have a tendency to catastrophise. Even the secure ones in well-established friendships seem to do it, and the ones that have had friendship knockbacks can be really quick to see the worst in a situation, which can in turn make it worse for them.
Is there anyone within the group she could talk to about it? May definitely not be the answer, but a thought!
Any other kids in similar situations she could team up with? I listened to a podcast about teens and friendship exclusions recently (It's called the askLisa podcast), which had some helpful ideas about looking for the other kids who are in a situation where they want friends, rather than trying to break into established groups.
Does she have good things going on outside school? Anything you can do to boost that - whether it's with friends or with you?
Would it help to 'just get to the Easter holidays'? It's only a week or two, depending where you are, and could have a bit of a reset/try to approach some of the friendlier kids to meet up etc then.
Reading back, I feel sure you will have already thought of all that. I guess something to hold in mind for yourself, and for her to if she can, is that this is just a phase of life. Lots of people have a shit time at secondary school with friendships and go on to have good friendships and relationships. I know that doesn't help when you're in it, and living it, but it might help you to hold on to that as you try to support her. And do what you can to support yourself so you're able to hold her feelings about it all without managing yours within your relationship.
I hope someone else has some proper advice soon, and you're both holding up today.