Being good mother-in-law is a problem?

Hai llites,
My mother is a very good mother in law. She never saw her daughter in laws different to her daughter. I have three bhabhis and two of them treat my mother as their mother and the third is the new one. She is pregnent now. My mom asks her to take meals, drink milk and juices and takes all care a mother has to take care. Even though she has the problem and told her parents that she is being tortured. And now she is in her mothers place as my brother is out of India on job purpose. And she does not want to go to my brother after her delivery also. My brother asked her to apply for passport and after so much pressure she agreed and applied last week. She shows her self good to all in the public meeting. My big sister-in-laws talked to her in this matter that why are u behaving in such a way. We all can stay happily, we have no tensions, no money problems, etc. But no use. She doesnt care to reply my brothers e-mails and reply to his calls.He is very much in worry.
Can any one suggest what to do.

Sangs.