I'm so sorry someone took advantage of your mom like that. I would say call the police and the Attorney generals office of your state. Sadly, she will probably never get that money back but to help prevent this from happening to someone else it should be reported. I would also suggest going to the local newspaper with your story, it could stop someone from making the same mistake.
Someone tried the Nigerian scam on my sister, but she is sauvey enough to know she was being scammed. She got the guy to send her the checks he wanted cashed and she immediately contacted the police who turned them over to the FBI. They didn't get the person, but they were able to trace to the source of the mail which put them closer to finding the scammers. I guess every little bit helps.