Joint mortgage- one co-borrower won’t buy other one out

My son and his girlfriend got a first time home owner loan for a house. They broke up, she wants to keep house, but refuses to buy me out. She can’t refinance alone and doesn’t want to pay higher interest rates. How can I get her to sell the house and give me my share? Is hiring an attorney and taking here to court the only way to resolve this? I also heard she doesn’t stay there and has other people living there paying rent.