MYOB ! Don't loan them money yourself.  that is the extent of your business in this situation.  You are not your mother's boss.  She is free to do as she likes with her money.
My Son in law has a similar situation in his family with his older brother, who at 40, is divorced, behind in his child support and rent.
The writer can't let this situation affect his/her life.  Walk away and live your own life.