Purdah from mothers husband
Q: Should a baligh girl observe purdah from her mother’s husband even though they may never get married. To what extent should purdah be between them?
A: With all the fitnahs and suspicions that go around it is best for their respect and their modesty that they should observe some level of purdah, though this is not fardh.
And Allah Ta’ala (الله تعالى) knows best.