From a mom whose 36 year old and two grandkids moved out in May (after a year living with me) my suggestion is to, if you have to do this, sit down and make up a game plan with a time frame to move out and some house rules BEFORE hand. I wish I would have set some ground rules going in.
It was a pretty bad experience, partially because her two brothers still live at home, and none of us were prepared to deal with an out of control 2 year old and a nine year old (not to mention their mother who is a piece of work in her own right)
I never got involved in any disipline, or school work stuff, and only put in my two cents worth when asked, which was not often cause she didn't like my answers LOL When things with the kids were working up to a fever pitch, I just left the vicinity
But it is definately tough with two moms in the house, especially if its been a while since the older one had to deal with all of the "stuff" that comes along with having children in the house again,nevermind difficult child kinda stuff
Good luck - gotta tell you that at 56, there is NO way I could reside in the same house with my mother LOL