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The closest thing I could come up with to match what Raffee heard is:
… she walked into that which was his.
Seems like an unnecessarily complex construction though. Tromboniator’s suggestion works better.
Raffee: Saying “… she walked in his” doesn’t work because that changes the meaning to “where she walked” instead of “where she entered/arrived.”
The words “in” and “into” are both prepositions, and sometimes get interchanged, but the meanings are definitely different.