I noticed that both of my older kids needed to start wearing deodorant at around the same age as your DD.
It wasn't like they had overpowering teen/adult odour, it was just a more stronger smell than usual. I would notice it majorly when picking them up after they'd done sport or it had been a hot day out.
Their smells change a lot when they hit full on puberty - for my kids, this was age 12) but in the mean time I think it is definitely advisable to get them used to wearing some kind of deodorant. My DD1 uses the Rexona Girls stuff and it is pretty good.