On 12/25/2014 Susan Louise said: Why not just ask...When did/do you plan on leaving?
No no no no! Not a good question to ask. That's giving HER the option to reply any way she sees fit, and you probably won't like the answer.
I have no solution that hasn't already been mentioned, some of which are really funny. I feel for you, but as many posters said, it's really your husband's responsibility, and he's not doing what he should. I know you mentioned there's more to this story, which there always is, but he's really being unfair to you. The both of you have to be on the same page and agree that she's got to leave by such and such a date.
I know it was mentioned to cut off her food supply. Is there any way to cut off her air supply as well? 
Good luck!
"That's a great first pancake."
Lady Gaga, to Tony Bennett