I know you've already got your answer and have met her, but I'll still chime in with my experience here.
I always want to meet the partners of my partners. You can tell a lot about a person by the people with whom they choose to form relationships. I don't like to be some faceless "other woman" and meeting me helps them see me as a real person. I also want to make sure they aren't cheating on their partner, and meeting the partner removes any doubt of that.
When I started dating my girlfriend, her husband insisted on meeting me "before naked happened." I was fine with that. Now her husband and I are friends. We both sew and we have fun talking about that.
While it's not always the case, it often happens that people tend to date the same type of people. That means that there's a good chance your metamour is someone you can be friends with.
In my case, meeting my metamour worked out extremely well. He's gone to bat for me at times where my gf didn't approve of something I was doing. He showed her the situation from another angle and literally fought my battle for me, before I even knew there was something we had to discuss. By the time she told me about it, it was more like "I was upset with you because of ___, but I talked to Chris about it and he made me realize I was being foolish. I'm over it now, but I just wanted you to know what had happened."
Gralson: my husband. Auto: my girlfriend.
Zoffee: Auto's husband. Cue: Zoffee's boyfriend. Bookie: Cue's wife.
"A real relationship doesn't properly begin until the NRE burns away. That's when you have to start dealing with this person as an all-around human being, replete with irritating little habits. When disillusion sets in, love can begin."