Anna should download a BCH wallet which has BTC wallet support too. She will going to use the seed phrase of her BTC to access the BTC address where she uses to send her purchase BCH. There are instruction in where other wallets could retrieve those BCH stored in BTC address. There were mentions about recovery tool that can scan and transfer BCH coins from BTC address to the BCH wallet.

This is a little bit complicated for me since I can't speak about the technical aspect of wallets but these are the only ideas that has derived after making some google search engines. I just overlook this before and didn't care at all because I am confident that I could not get mistakes when transferring bitcoins or any alternative coins like BCH. So, this could be a  perfect time to ask or see the possible answers I could get in the OP riddle. I think this is not literally a riddle but more on an application of ideas learn about bitcoin and wallets.

Anyway, I was happy that I get the right answer it was a bit easy for me but the follow up question was a little bit difficult to my current knowledge about cryptocurrency.