My husband is in the army and his 11 year old daughter came to live with us in April. The mother has never carried a stable job, and has moved away from her other child(different father) and boyfriend to who knows where... She has yet to contact her daughter or even acknowledge her birthday, she gives her numbers via email that are incorrect or un answered.. I had heard from someone that there is a way that if she doesn's make any contact with her daughter for a certain amount of time that there is a way for me (her step mother) to get rights as her mother "legally" because her mother has "abandonded" her rights. She is not paying any child support nor did we ask her too, she is also unemployed. Is this true that after a certain period that I may do something to get legal rights and not her mother? If so how can we do this?

No, she will never be "legally not her mothers till you go to court and get the custody changed legally, and also get the mothers rights taken away if possible.