There may be several reasons why an elders wife remains after he leaves. Three that I can think of are....
1. He has seen first hand,over an extended period of time, the inside dealings of the organization. Heard the problems, seen the personality clashes, dealt with the power struggles and egos. Most or all of it, until now, he has had to keep silent about. It would be difficult to convey to her all the subleties and nuances of the conversations and the dealings he has been part of over the years and expect it to have the same impact on her.
2. She has enjoyed the status of being an Elders wife and because of this has had a good share of attention and has been able to make friends and be a bit more popular than the "plain" JW. It might be hard for her to just leave because her husband is burned out. Maybe he'll come back, she hopes. In the meantime she may get to enjoy playing the part of the long suffering Martyr.
3. When you look around the KHall in general, there seems to be a larger proportion of Women with unbelieving mates than there are Men with unbelieving mates anyway. That tendancy already exists. I think Women are more inclined to want to be part of a community and may allow untolerable circumstances to continue because of that desire, than men are. (I'm generalizing here) Women gather together and commiserate with one another ...Men tend to be loners and want to handle things themselves.