AF started for me at 11 and I know BO/hair/etc started at least a year or 2 before that. Last year I had a year 6 class and made sure they all knew there was a deoderant in the cupboard for when needed (and showed them how to clean it before/after use!). It didn't get used much but it did mean we could openly have the "you need deoderant" conversation, as I knew throughout the year most of them would start needing it if they weren't using it already.
I'd get a roll on and a spare to keep in a internal pocket in her schoolbag (eg. for after sport etc if needed). Spray deoderants/impulse etc are ok at home but you will probably find they are banned at most schools due to being a potential asthma trigger.