Hi Dee! I'm sorry for this horrid mess that your SIL has created for your family. I have some experience in this sort of behavior, and I'm getting more as I took a position in the hospital.

You have done all that is humanly possible in this case except one thing:
Your husband must call the police as well as adult protection should her mother be hurt by her one bit.
To continuely have her arrested is the point to which her life has dropped.
It's hard to call the police and insist of pressing charges when it comes to family, but it must be done. Laws now do not require your MIL to press charges, the police have that authority now.
Were I you, and it's only my idea, I would hope that she did get arrested and more than once so the judge finally puts the law in charge of her rehab.
Some people do not listen to anything in rehab unless the police take over:\
Paris Hilton,
Robert Downey Jr.

She belongs off the street, out of society and paying for her damages. I know that what she has is a disease but to make a person take their med's often requires a court order and consequences if they fail.

What do you think? Would your husband have her arrested if he found that she had struck your mother? It would be the best all around. If she comes to your home and causes a distubance, I would vow to call the police in that case as well.

Dancer9, seeing addicts in action in my career.

(I've had to have my mother arrested three times to get her medicated (she threatened her life,) and she has had to be court ordered still to take care of simple health problems. She is schizophrenic.)