Oh bless her. It can also be difficult, especially if PE is anything like it used to be with showering when I was at school, where it is more obvious to others who has hair or not or removed it and can be embarrassing and girls can be cruel.
I'd let her shave it, with help at first if she wants it.
If she is feeling self conscious about the body odour during the day then, as well as a roll on, she could get a nice fruity spray, they do them in Primark and Superdrug/Boots, Body Shop etc... which is a bit nicer than using something more chemical like an aerosol antiperspirant or more perfume like such as Impulse.
Creams can be difficult. My skin is quite fragile and I have stayed away from them after a few unpleasant incidents (especially on the face) and one literally took a chunk out of my leg once.