Hi A. - the stinky part of BO is from bacteria on the skin - sweat in and of itself doesn't have an odor. If the bacteria are dealt with, the odor is often taken care of as well.
Hormonal variations can have an impact on sweat glands and how much kids and adult sweat. There are a lot of natural mineral deodorants on the market but you might also consider something as simple as washing her with weak hydrogen peroxide solution - 1 teaspoon in 8 oz water. Wipe down her underarms, feet, groin (the crease at top of thigh - not her private parts)
My two year old was really stinky suddenly and this worked like a charm. I found this idea on WebMD.
Since your daughter is only 7, she probably won't remember to wipe down at school although you could send some wipes in her backpack to use after gym class, etc.
Just do a wipedown in the morning on her underarms, groin, feet and I would imagine you will see a quick improvement.
I'd love to hear back if this works for you!