As salam u 'alaikum... If a person is married to a widow who had a daughter, does that girl need to maintain hijab in front of the father of her step father?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The daughter of the wife from another man is called a step-daughter. If a man marries her mother and he consummates the marriage with her, then this stepdaughter becomes a Mahram to him as Allaah says (what means): {…and your step-daughters under your guardianship [born] of your wives unto whom you have gone in [are forbidden for you to marry]. But if you have not gone in unto them, there is no sin upon you.} [Quran 4:23]

However, she is not forbidden for his fathers (father, grandfather, great grandfather, etc.) to marry. Based on this, she must wear the Hijab in front of the father of her step-father as he is a non-Mahram to her.

For more benefit, please refer to Fatwa 84424.

Allaah Knows best.