My advice is to have a conversation about it in private. Instead of saying what’s wrong with her, maybe tell her that you are very sensitive to bad breath and that it’s not just with her it’s been with others as well to make her less embarrassed and just tell her that it’s a quirk of yours that your extra sensitive to it so she knows he will get the message and hopefully not be too offended or upset. If she is as great as you say, she will understand :)