I may be biased because I have been a legal guardian of a little boy for over 4 years. I've had him since he was 1. He began calling me mom when he was about 2-2 1/2. I know this was hard for his bio mom, but his therapist said that I should allow it and not correct him. He knows that he has another mother. It is really confusing to a young child who is being raised by someone (and bonding to that person as a mother figure) to be told they couldn't call that person mom. He needed to relate to me that way. He needed to feel that bond. He needed to rely on me as a mom. As much as it hurts you (I can't even begin to imagine that feeling) try to remember that it isn't something that is being done to hurt you. It shows that your daughter has a very strong bond with the mom who has been consistant in her life for the majority of her life. I think you need to really search your heart for what you feel is truly right for your daughter. I don't know your situation so I don't know what is right. It sounds like you are doing awesome now. Six years ago you made a decision that was best for your child. It is obvious you love her very much. Now, try to step back from your emotions (not an easy thing I know) and try to see things from your daughter's point of view. She has spent most of her life in another state, being cared for by someone else. You are obviously a very important person because you are her Mom, but does that mean that uprooting her entire life after so long is what is best for her? What kind of trauma will that cause her? Could it possibly be better for her to remain where she is and you visit and call more often? You could build your relationship back slowly and have a different kind of mother daughter relationship. She need to know you love and want her, but she also needs to know that you care about what she needs/wants. I'm thinking about it from my perspective as the "mom" of someone else's child. I can't imagine what it would do to him to be taken from my home. (That isn't even thinking about what it would do to me and my other children which is a totally different consideration all together.) If his mom ever got her life together as you have, I still don't think that being with her is best for him. He has been with me most of his life. Living in a family involves so much more than who is caring for the child. Parenting styles, family routines, the way things just naturally go are all things that people (especially children) find comforting and secure. Of course you want your daughter home. You love her and miss her. But is that best for her? For your relationship with her which is going to last for the rest of your lives, not just her childhood? For her sense of security? Sometimes doing what is best for your child is the hardest thing you have ever had to do. Don't make any decisions based only on emotions. Try hard to look at different viewpoints and options to work for everyone.
Another thing to consider if your mom is refusing visitation is to petition the court to order visitation. You could get time with your daughter without the drastic changes that a change of living arrangements would entail.