The easy and quick answer would be to hire an attorney who specializes in fraud and contracts, contact the attorney generals office in your state, contact the agents broker, contact your municipal consumer affairs office, contact a reporter (they love juicy stories about fraud) contact the national association of realtors.
That said, your question leaves some doubt to its' legitimacy. Don't get me wrong on this next point. I have dealt with a lot of fraud in real estate and have seen some pretty good scams. Just about anything is possible. However, the idea that your X, could lose her home and all her money because of a realtors mistake sounds a bit fishy. Possible but I'm skeptical. If it is so, sounds like a good fraud case for someone to go to jail over.