“Because it’s ben acher ben from the Chasam Sofer but not from Rav Akiva Eiger.”
Please reread the OP:
“My great grandmother,Rochel Waisfogel was a grandaughter of the Chasam Sofer, but we have no clue who was her mother, whoever knew is not alive anymore for us to ask them. We only have the matzevah in which it’s written Rochel bas Gedalia, nechda of the Chasam Sofer, ”
Perhaps you meant to say, “bas achar bas’?