It is not unreasonable to have her start to use an underarm deodorant at this point. If you are concerned about irritation, use one that is just a deodorant, without the antiperspirant (The aluminum chlorhydrate that's used in most antiperspirants is the ingredient that tends to cause skin irritation). If you don't want her to use deodorant, consider using a body power that has baking soda in it. They are available in most stores and come in unscented varieties, so that you can avoid a perfumy smell. Don't put the powder in the genital area though, just use under the arms.
Is it normal for a nine-year-old to have body odor?
I have a nine-year-old daughter who is beginning to go through puberty. The hormonal changes have made her body odor uncontrollable. Needless to say, this makes her self-conscious and embarrassed. We have taken every measure we know of to keep this under control, but it doesn't seem to be working. Regular showers are good for a couple of hours, cleanup in between is the same. Please give us some advice as to what the next step should be.
This is not an uncommon problem for girls and boys as they get to this age. As you suggested, the sweat glands are stimulated to enlarge during puberty in response to an increase in certain types of hormones. The body odor can be very strong. It is important to encourage children to bathe daily and to change their clothes, including socks, every day. The days of wearing an outfit for more than one day without washing it are over! Also, watch out for smelly feet, and make sure she wears something other than sneakers all the time.