You can't force a friendship with anyone. You've invited her to spend time with you. If you want to continue inviting her then go ahead, just try not to invest too much in the answer if she doesn't want to spend time with you.
As for your primary and his girlfriend their relationship is going to develop in whichever way it's going to develop. There's nothing you can do to influence how people feel about each other. Also it's not about loving one of you more than the other, it's about different and complex relationships. Primary doesn't always mean being loved more. A lot of the time it has more to do with time spent together and other life type enmeshments like finances and children.
Let it go with her. You don't have to be friends with metamours (although that would be ideal). Let them have their time and their relationship and just focus on how happy your partner is. Maybe she'll start hanging out with you and maybe she won't. In the long run it really doesn't matter unless you're all planning to live together.
Everything will be ok in the end. If it's not ok it's not the end.