Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear questioner, we would like to thank you for the great confidence you place in us, and we implore Allah Almighty to help us serve His cause and render our work for His Sake.
Responding to your question, Dr. Salah Al-Sawy, President of the Shari`ah Academy and the Secretary General for the Assembly of Muslim Jurists in America, states:
The wife’s mother becoming Mahram is a permanent status that has nothing to do with the continuation of the marriage or its end. She (i.e. the mother) remains a Mahram for her daughter’s husband even if he divorces her daughter.
Allah Almighty knows best.