suing for sole ownership of a dog

[MsMaJik]

I bred and co-own a dog who I've had since birth (i am her breeder). The owner of this dog's sire co-owns her. I have had her all but about a month of her life. For a short period she stayed with her co-owner. Now she is back with me and has been for about 6 months. Now the co-owner doesn't want to home her, pay for anything to do with her, and wont sign papers over to me. She says the dog has a "soft" temperament and needs to be spayed and placed in a pet home which is not the case seeing as i have had her most of her life and she is a beautiful specimen and would make a fantastic show dog. I am really trying not to get legal about this but it seems she is leaving me no choice. So what are my options? there is no contract between she and I and she forged my signature on the dogs papers. Ive never even seen the papers because she has possession of them.
thanks in advance
Alexis (PS we both live in California)