I emailed my old boss last night as he was a lawyer who helped people who had been in car accidents or bitten by a dog, etc., get the $$$ they were entitled to
NOT, NOT, NOT the lawyer you want. Mary, you absolutely must get a lawyer; however, you need one that specializes in disability insurance.
Until such time as you obtain representation, you can take preliminary steps. You can ask the insurance company the following: What medical basis do you have for discontinuing my sister payments? Which physician has said my sister can work? It appears that your sister has a preponderance of medical evidence on her side. This should keep her payments going for a while...long enough to get an attorney.
But prepared, they will OBTAIN medical evidence to support their contention that your sister is able to work (ATW) by sending her to an independent medical exam (IME) with one of their doctors. Usually, the terms of the contract state that she must attend to exam or they can discontinue payments.