First things first, why won't she try to confront her in-laws about the situation. she is now their son's wife and knowing that fact, the in-laws should understand what she is capable of doing and they should also know the boundaries between their son's life now. She must do a thing about that because she is the legal wife and she has the right to voice out what she is feeling. Of course, confrontation does not have to argue. Try to talk it out in a constructive and nice way. I will do that if I am in that situation with confidence!
Second thing, if they don't have a problem as husband and wife, then it is just a shallow reason to leave her family lest her husband. If her husband keeps on ignoring her about her situation with the in-laws maybe the reason is that he doesn't want to cause any further troubles or the like. Again, it is up to the wife to know how to literally communicate with him.
If the situation is helpless, I might as well choose to leave but together with my kids and with my husband (assuming that he will go with me) away from his parents. It would be better that way. I think.