Hi Poppy,
My daughters father ignored her existance until she was 4 - and it was me who initiated seeing her, Your problem is a similar one to mine.
He did see her every week for a couple of hours, then when he got married had her overnight, one night a week, and dropped her back first thing in the morning. This went on until she was 15. He saw her boxing day 2009 and she never heard from him for 6 months. He tells his family he phones, but she doesn't answer........the truth being he doesn't even have her mobile number.
It is a long way of saying that, if your daughter accepts that she is not seeing him, I would not force anything. I have always said that I will not lie to my daughter about what happened, but I don't need to tell her anything she has made her own mind up and is alot happier not seeing him and being told how brilliant her little brother is. Of course she misses her little brother, but the day will come when our girls are old enough, if they wish, to confront their fathers themselves. And we will be in the knowledge that we have done everything for our girls and they will make us proud and the fathers will not be able to say that.
Don't fret for your daughter, just be the wonderful mum that you are and enjoy the time you have with her. Leave him to his own life, he is the only one who will regret it - honest!