Thank you for coming to our forums. This is indeed a tough situation, and I can't offer you much advice, but I can perhaps offer a different perspective. This is still a pretty new relationship (4 months). Many secondaries struggle with their role, and are often apprehensive about possibly causing problems with the primaries' relationship. In my case I actually met my metamour and had dinner with him and we discussed our situation frankly, because he wanted to make sure I actually WAS OK with things, because prior to this he only heard things as filtered through my wife. After our meeting he was a lot more comfortable. I think it's good that she communcated directly with him, and you may want to encourage more of that.
She's definitely dealing with some tough issues with her ex, and that's something that you can't solve for her, but you can always be there to listen and sympathize as much as you can. That being said, it's entirely possible she's actually pining for a new father for her daughter. It's pretty common in situations where a mother leaves a bad situation to try to find a much more sedate, normal life for their child. It's a pretty strong biological drive.
It's also very possible she is feeling guilt about being in what she sees as a relationship that is benefitting her and not her daughter. She may be feeling guilt for taking time for her own needs and think she's neglecting the tough job of finding a father for her daughter.
Again, these are only speculations. I don't know her like you guys do, and I'm not a trained psychologist. Perhaps some better qualified folks will come along and give you some more focused and qualified direction.