We don't know the entire story for sure. But there are bits and pieces of the story from her MIL's friend/neighbor's version. Taking it from the MIL's friend/neighbor, it is obvious we give benefit of the doubt to Mrs M. And, we have seen many Mrs Ms in real life too. So, this story doesn't come across as something unnatural. Mrs M's in laws go to their son's home for resting. Mrs M's mother is not allowed to visit or stay in the US with her DD, but she had to stay with her brother's family despite of having raised a child of hers. But the same mother is now with Mrs M in the US after her separation. There are certain threshold, after which women loses their tolerance level. For some it is their kids's safety/well-being, for some it is their relationship with FOO, for some it is their self-respect etc.... You can't force a woman to take care of her PILs, while her own parents are left to die somewhere else. Perhaps this is Mrs M's tolerance level it seems.