Hubby & I were in a somewhat similar situation recently, although it was my gf who moved in, and it was due to her relationship breaking up with her husband. We really didn't even expect her to contribute financially - we wanted her to save money so she could get on her own two feet and support herself, but unfortunately, I think she thought she was going to stay with us forever. (Not only that, but we had VERY different ideas about what constituted a clean house). Things would have gone much better if we had set better boundaries early on. She never really got a good job, and we actually directed her to another friend looking for a roommate, with whom she moved in, but the damage had been done. Both to our own household and my relationship to her.
I know you probably can't stand seeing two people you love crying and upset, but it seems like your good nature is being taken advantage of. Come up with some reasonable ground rules and perhaps even a timetable of sorts for her to find a job or move on. It's hard, but the primary relationship with your wife is really what counts, and your own needs count too.