I am trying to get some information to assist my mom (70) with a work related issue;

She has worked for the past 10 as a part time employee earning a little more then minimum wage on Cape Cod for a big national retail company. Lately she has had some health problems and has been out on excused sick leave on and off over the past six months. Her supervisor gave he a written notice warning her that she has been out rather frequently and could be terms for dismissal. What puzzled her the most was that the supervisor warned her that it is now her responsibility to find another employee to fill her schedule if she was going to be out on excused sick absence and that it was a Massachusetts state law for her to do so and that the company was within the rights of the law. If she failed to do so she could be fired. She asked the supervisor if this was company policy or law, the supervisor responded that it was state law and she could confirm it with a lawyer. She also asked how she should contact the other employees and was given no answer. She asked for a call list but was refused.

I find this difficult to believe, the scheduling sounds like a management responsibility and that the supervisor was using bullying tactics on a senior citizen pressuring her to quit. Are such management tactics permissible?

What recourse can she take and how should she peruse this?

It isn't a law but it really doesn't matter as the company can insist that she find a substitute when she is going to be out and it is entirely legal. Being a senior citizen doesn't give her any additional rights or privledges.