Moister wicking, breathable clothing.

Epsom salt baths!! Let her soak and relax at night. I had bad BO when I was pregnant with my oldest son.

I remember as a teen that certain fabrics plus my sweat would equal a really strong odor. I can’t remember which but it was a blend. Not sure if you’ve noticed any patterns with what’s she’s wearing and how bad the odor is.

Make sure she's drinking tons of water too! That does make a difference

I can only respond as an adult deodorant user, lol. With the liquid and gel deodorants, I always have to apply a few times throughout the day, so now I only use the solid sticks. I loved the teen spirit lady speed stick when I was a teen.

If the doctor does hormone checks and all is well, one thing you can ask about is having her use panoxyl for her armpits. She can lather up her armpits with it, let it sit for a couple minutes and rinse it off, then shower. Benzoyl peroxide is the generic name, so any one will be fine. This kills the bacteria and prevents body odor.

Body odor is caused bacteria on the skin, I think eating the sweat and then the odor is the product of that. There's a lot of diy stuff, but this might be best for her because it's really straightforward.