My granddaughter recently had a smell issue, which I believe was no body odor, but her breath. I don't know why, but she smelled like a mixture of rotten fish and skunk. Please help!
Avoiding the obvious smart ass responses and treating this seriously - It most likely is her diet. Something she is being fed, she is having difficulty digesting. I would take her to the doctor to confirm this, as she may be lactose intolerant or have some type of food allergy.
Also, you could try getting peppermint oil capsules and have her take one before bed. They aid in digestion and are natural.
Try a different toothpaste and mouthwash, maybe.