I had a couple possible ideas. I'd love her best friend since childhood. He stuck up for her when she was being bullied (maybe even threw a punch or two in her defense if that's the kid of person he was). They've always been there for each other. And we could develop it from there.
Or I've toyed with the idea that she got married for a few months when she was really young. It didn't work out and she doesn't talk about it, but now they can be in the same place for the first time since then?