Funny. I was thinking about this today. I used to babysit for a dad who told me about a similar situation and how he handled it.
He was dealing with a clerk at a store. He quietly and genltly said, "I don't want to hurt your feelings, I am saying this to help you. Ask a close friend about how to keep yourself clean and fresh. If they love you they will walk you through it. If I didn't care about your wellfare I wouldn't have said anything. Please accept this as a step for positive growth."
I know this situation is different cause you have a relationship with her. Perhaps it will give you some ideas. I think she will think more highly of you if you mention it rather than avoid the issue or try to manipluate your way around the situation.
Good luck. Be a good friend.