My friend smells terrible, what can I do?!?

She's had a few problems at home recently and I feel so sorry for her, but she's really let herself go. She has breath that makes me feel physically sick (so bad I have to cover my nose when talking to her, as subtly as possible of course), absolutely terrible BO and her hair is just dripping with grease. People are always making fun of her, and I don't know what to do. I haven't tried to bring up the other issues, but I tried to ask her subtly how often she washes her hair. She said that her hair doesn't get dirty easily, and she only washes it once every 8 days or so. It's revolting looking! Nobody on planet Earth can go that long without getting greasy hair and she doesn't seem to realise that. My Mum has suggested giving her mints and stuff, but I can only do that for so long, before she gets suspicious. I really do not want to be blunt and tell her straight, as she's so upset already and it would destroy her. I can't put up with another year of this though, I'm dreading it every day! Please give me some help!!