I was the one with the bad attitude with my husband's last girlfriend. I think it was because she was timid around me and I fed off it. Eventually we came to a place where it was just better that we didn't spend time with each other. I was perfectly happy for my husband to have a relationship with her but realized that this was someone who I would never mesh with myself. I didn't like the person I was when I was around her. So limiting our time together was best for everyone involved.
Sometimes people just don't get along and that's perfectly ok. As long as you can respect her relationship with shared partner(s) there isn't any reason it has to go any further than that. Rather than trying to fight an uphill battle of being friends with someone that if you didn't share a partner with you probably wouldn't befriend put your effort into friendships that lift you up and make you feel good about yourself.
Everything will be ok in the end. If it's not ok it's not the end.