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 stuff for her. All kinds of stuff.