Is this considered kidnapping?

My gf (now ex as of yesterday) took our daughter to another state with her for what was only supposed to be 2 weeks - but what slowly became 2 months. We were never married and I need to know if I can get her for kidnapping or if there is really any chance I can get full custody. They moved to a very bad area in South Dakota & I live in California. I AM on the birth certificate, my daughter has my last name, what can I do about this?