Help!!!a

My mil so far is mostly kind to me but horrible to my SIL her other daughter in law. She has alienated them from the family and tells everyone she's crazy and horrible and makes jokes about taking away her baby. My SIL has pp anxiety and depression and my mil refuses to believe it and is horrible to her and refused to respect her rules with her child so they cut her out of the baby's life after months of trying to find a middle ground. But my SIL and I still have a very good relationship and it makes my mil very mad she tries to use

Me to get to them and get access to the baby and gets mean when I refuse. She's extremely controlling and gets mad and me and my husband for making life choices with out asking her and she constantly mocks us for being independent. We're moving for school soon and will end up closer to my SIL and BIL and she's been really mean and passive towards us because of it and keeps saying how she knows we're making a mistake and jokes about being able to visit us and bug her son and other daughter in law and try to force time with their son. What do I do???? Iv tried so many times to let her know that this is not ok behavior and that I don't like her using me to hurt my SIL and that my husband and I are adults who make our own decisions. But she won't listen now I just ignore her completely if she says anything involving my SIL and BIL but it just makes her freak out even more

------UPDATE-----

My husband agrees with me that it's not ok behavior and that his mom need to figure some stuff out. We have decided to talk with her one last time and let her know exactly how we feel and exactly what we think she is doing wrong and then we are going to create some distance between us while we see if she even tried to change. We also decided we won't ever completely cut her out because his father is a very sweet man who has done nothing wrong, and he's just so tired and sad and worn down by everything she's done lately and we don't want to alienate him and make him feel as tho we don't love and care for him. As well as my husbands younger siblings still at home. But as for her we plan on being polite but extremely blunt and firm in what we are saying and what we expect.