Dating someone with a child (HELP)

I've been dating my boyfriend for about 4 months now and he has a daughter. I adore her and see her as my own. This also isn't our first time being together, we first dated 3 years ago but decided that we needed to figure things out before being together. I need some help from other women who are in this same situation, the mother of his daughter won't even look at me. Any time we meet she acts as though I am not there. His daughter has already began to mention why her mommy and I do not talk and asked if I would please tell her hello. Of cousrse I did but still got now response from her. I want to have a good relationship with her for the sake of the child. Any help please