Should I help two people (my husband and my daughter) have a better relationship?

My husband and my daughter (his stepdaughter, who is 19) have a precarious relationship. They are both beautiful, amazing people. However, having been through her teenage years, he sees her as she was (lazy, irresponsible) and not as she is becoming. For her part, when he addresses his concerns in a normal way (no yelling, but expecting responsibility from a 19 year old) her feelings are hurt and she wears her heart on her sleeve. She is emotionally immature for a 19 year old. I’ve grown weary of trying to explain them to each other and trying to help them have a good relationship. He wants to, but she runs away emotionally. Should I just bow out and let them figure it out or keep trying? I dearly love them both.