She is probably still working through her hurt that she is feeling of why she was given up for adoption. I can understand why she would be reluctant about building a relationship with your Mother, but you had nothing to do with the decision, so you would think she would be excited about finding a sister.
I would mail her cards and photos, on every major holiday, and just leave the ball in her court. I would think that one day she will finally give you a call to learn more of her bio side of her family, and build a relationship with you then.
Good luck, Hope