She needs to recognize that the money supply has ended. It only came from the selling of an asset - that asset is gone and she was given the larger portion of it. Your mom's SSDI is for her and her only. It sounds like your sister finding out that your mother helping you was a big mistake and I'd start with reversing that by whatever means necessary. If your sister doesn't think there is money to be had then she won't be attempting to take it. She's essentially threatening to sue you in order to commit fraud. It's an absurd thought. She's also threatening to [assumingly] lower your mother's quality of life for her financial gain. That is extremely concerning.