I've been on both sides of the fence--as the new love and ex-wife. When I fell in love with a custodial parent, we decided to live together. I didn't press for a meeting with the ex. It happened naturally, and we respected each other's position in the child's life. We were never best friends, but we could get along.
When I was first the ex-wife, I told him not to bring her around (he left us for her). The one time she and I met, it was forced by circumstances. Unfortunately, I'd learned some very ugly things about her, and she lived down to every one of them. No way could she and I ever get along. My daughter never met this woman.
I was also forced to meet Wife #3, due to circumstances (my daughter's aunt's funeral) beyond my control, and it was very awkward. I don't know if she and I would ever get along, but living in different states has prevented that from being put to the test. This meeting was also very awkward for my daughter, who was 17 at the time. Her father's ll years of chosen absence from her life probably didn't help things either.
I would do my best not to force a meeting with the ex's new partner. If I'd been the new partner, I'd not have rolled the window down either. I do understand your curiosity about her though. For your child's sake, I hope she's a nice person with a lot of good to offer the little one.