This is just my $.02. And it's based on my history, so take it for what it's worth.
My mother divorced my father when my sister was 16. Things were rough between them after that. Did my sister deserve a mother? yes. Did she have one? No. Was my mother a bad person? Well, that one is hard to answer. My mother certainly feels guilt now, though the guilt is buried beneath layers of hurt formed from poor communication between the two. I also have layers of hurt but that's a different story. Point is, they never figured it out.
Tawny doesn't have an adult woman in her immediate life right now and that's just the way it is. She may identify someone as a mentor in her social life, she may figure something out with Carrie, or you may meet someone new that she bonds with. But it is going to be her responding at the pace of her own needs. The only thing you can do is be the best father you can possibly be. Which you're doing.
I know it's frustrating, but you don't have control over the relationship between tawny and carrie. They have to work it out and you have to take a supporting role. And be damn good at it. IMO.
