I was going to say as pierceing star said offer her a mint. Other suggestion talk about your favorite toothpaste and tell her she should try it or just buy her some tell her it is very mintie refreshing.
There might be something wrong that her dentist or doctor can help with. Tooth decay or an infection will create odor. Overactive tonsils (if she still has hers) can collect bacteria but then not take care of all of it quickly enough. Certain foods can linger; onions and garlic are the typical culprits, but there are others. If the two of you are good friends, she'll appreciate your concern, although she'll probably feel somewhat embarrassed too. Pick a time when it's just the two of you and say that you have something to tell her that she might not like to hear but you think it's important. Check this web site: mayoclinic.com/health/bad-breath/DS00025/DSECTION=causes for more information about various causes. There's also a page that lists home remedies.