I think encouragement is a better way to go...telling a disabled person that you wont put up with their crap(crap in reference to their disability and things it interferes with) and to knock it off or leave essentially that is just going to come off very invalidating and mean.

I mean she has obviously mental illness serious enough to take meds and cerebral palsy....I can see such an individual feeling down about things and not doing a lot of physical activities on the weekend, especially if they work during the week. So encouraging therapy is good provided shes not completely destroying the household and being abusive then I'd say certainly do what needs to be done to have her move out....if she is severly dysfunctional to the point of neglecting her needs or things like that she might need more than therapy.