Has she tried contacting you since you moved? I'm not sure why she's fixating on you but I do wonder what your boundaries have been like with her. If it's been inconsistent or weak, now is a good time to firm them up and I think she needs to be told what those boundaries are.

How are you related to her? Where are her parents in her life? It sounds like you've taken a parental role but are not her biological mother. Is this true? If so, could she be feeling strong emotions about her mother and taking it out on you?