Dear Kollel,
The following question came up in the shiur:
If I marry a lady with a daughter from a previous marriage, I cannot marry the daughter, because she is my wife's daughter, even if I divorce my wife.
If we have a daughter together, I cannot marry the daughter, because she is my wife's daughter and also because she is my daughter.
If I divorce the lady, she remarries, and has a daughter with the next husband, can I marry that daughter who is my [former] wife's daughter?
I have not found this case in Shulchan Aruch. Do you have a source for the answer?
Moshe Perkal
Harav Tzvi Pesach Frank (Har Tzvi, beginning of Yevamos) proves from Rashi and the Rishonim on our Mishnah that she is prohibited. Otherwise, a candidate for Bito that is not Bas Ishto would be if my wife bears me a daughter after I divorced her. He refers to Nehor Shraga who also discusses this issue.
I do not really see a question here, since the Isur of the Torah is "Ervas Ishah u'Bitah", "a woman and her child". It should not make a difference when she became her child. (Rav Frank also mentions this at the end of his discussion.)
Best wishes,
Mordecai Kornfeld
Kollel Iyun Hadaf