I would have never believed that adults could behave this way until it happened to me.
Our "Sue" was very chatty and warm seeming, but it did not take long to see that every conversation was turned around to her, she was in permanent victim mode which was used as an excuse for any bad behaviour, and that all in all, she was a pretty unpleasant person.
Almost immediately she started trying to freeze me out of the group, talking over me, turning her back on me, setting things up and "forgetting" to invite me. I thought at first it was oversight and tried to talk to her about it. That really escalated the behaviour. It really seemed I was the only person who saw it, and upsettingly, there was another person in the group I had a lot in common with, and was quite close to, who seemed to be taken with her. When the tensions started to seem apparent, this person told me she thought it was just a personality clash and I was as responsible as "Sue". Except it was not true - I am not perfect, but it was so obvious I was being bullied by exclusion and lots of passive aggressive digs. What I am is the truth teller who grew up in a narcissistic family situation and people like this can spot that a mile off, and will react negatively to it because it threatens to show what is going on.
Anyway, I had a very traumatic situation, and the group rallied round. Except for Sue. I took a step back from the group for a while because I could not deal with her while I was so vulnerable. Then a few of the other members contacted me and we met up. Turned out that they were disgusted with how she had been behaving, had been seeing it but not realizing how bad it was. She had been bad mouthing me with comments like "who does she (me) think she is", "(mutual friend) is MY friend, not hers" and "everybody has difficult things, you just have to get on with them" (her difficulties were things from 40 years earlier, mine was more in the nature of just being given a cancer diagnosis. I am not saying that her experiences were not traumatic, but it's not top trumps and at some point, other people have bad stuff happening and for normal adults, that needs to be a focus for a while).
Anyway, the group members started to distance themselves, leaving "Sue" to announce she was thinking of leaving. No one tried to persuade her to stay, which lead to a massive flounce. The only person hanging on to the 'personality clash' idea was the person I was developing a closer friendship with.
Happened to see "Sue" in the distance while meeting another friend who turned out to know her from another time and place. She asked how I knew her and whether we were close, so I said we didnt really get on and left it at that. My friend then told me "Sue" was very pretty at school but a queen bee and mean. Far from being bullied, she was the bully. She also moans that her local children dont see her often, but they are fed up with her. She also lost several jobs because of her behaviour.
Just keep on being you, dont confront her, dont lie to others if they ask you about it, but keep as neutral as you can. Grey rock her as much as you can, and concentrate on the other group members. They will either see through her in the end, or they are not worth your time and effort.