She asked me to get all of his private data from it and sell it. I have found a "bitcoin" folder there and a text file in it.
To get all the private key data is not from the folder file, but from aplication, bitcoin core wallet.
If that PC doesn't have Bitcoin core wallet yet, you may install from:
https://bitcoincore.org/en/download/ and run it.
You can disable network actifity on core wallet, if still catch the blockchain.
Then go to console, and write "dumpprivkey", that maybe have password you have to pass it before.
I have found a "bitcoin" folder there and a text file in it.
Have you seen the
wallets folder there?, I assume that text file is json setting file of wallet, not as key like your guess.