Also, consider having them read the book Presence by Amy Cuddy for some other concrete strategies to improve.
Try this: I wanted to share something with you that is a little personal, but it is something I want to make sure that youre aware of. Ive noticed [avoid saying that others have noticed, because that is likely to upset her] that there are times when you come to work where it seems like you might not be as fresh or crisp as wed expect. To garner the respect of your peers and clients, you want to project a truly clean and professional image. When it seems like you may not have taken the time to shower before work and use deodorant, perhaps, then it doesnt project that crisp image we should all be striving for. Id like to ask that you put in more effort to come to work each day as fresh and clean in appearance and hygiene as possible. What do you think of this request?