Don't stress. She can't do squat!
Think about it. What have you done with this mare? Shows, vet bills, board, farrers, friends all people who would KNOW that the horse has belonged to you for the past three years and would be able to come and testify for you (if it came to that). AND why would you ship out all that money for the sire for someone elses benift, i don't think so. AND if she doesn't have a court ordered you can tell her to get stuffed! Don't let her near the mare or your property. If she wants her she can have her repossessed. Did you pay for her?