Should I marry my loving gf?

My ex-wife had died 8 years back. I was left alone with my six year old daughter. I have been dating my current gf for last three years. She is a really nice girl and very understanding. I had decided to marry her and informed my daughter of my plan. She was very upset and totally refused to accept her. My gf had talk with her but she still refused to accept her as a stepmom. So what should i do? Should I marry my loving gf?