The said woman shall not turn non-mahram for her father-in-law after four months and ten days rather the daughter-in-law is haram forever for her father-in-law as per the Shariah. Hence after four months and ten days if the house is owned by the father-in-law and he wishes that his daughter-in-law should stay with him with his grandchildren and Shariah purdah is observed and there is no fear of fitnah then she may live with her father-in-law. She shall observe Shariah purdah with brother-in-law as he is non-mahram for her. And if there is no arrangement of Shariah purdah in the house then she should go to her parents’ home after passing iddah.
Allah knows Best!
Darul Uloom Deoband