Honesty and the ability to receive constructive criticism are pretty great things in a relationship. Since it doesn’t pass as ‘something I don’t have to cook’, I would just thank her a lot, and apologise but say I prefer it a bit more well done, and perhaps show her how I like it. Maybe mention the risks that come with undercooked chicken. I would also be infinitely grateful if she showed me nice tricks or just simply explain in detail how she would like me to do stuff for her. All kinds of stuff.