Yes, let her, but the suitable amount she is allowed to wear will be what you are happy with.
I would also recommend keeping a tight reign on what she wears, whilst being open to negotiation. Also strict rules that she is only allowed to wear it for school if it doesn't interfere with her getting out on time & eating breakfast etc.
I've noticed that DDs friends who were given free reign too young, are now the ones that a couple of years later, look like painted dolls with head-butt eyebrows - not a good look!
At that age, DD was allowed bare minerals powder foundation, which is light, natural, quick to apply, doesn't look caked on & is not harmful to the skin. She used the tinted lip balms such as Baby Lips, or EOS again natural, & tweezers & a little vaseline to shape her eyebrows
A few years later, shes a dab hand with make up, even makes YouTube videos on it & her look is generally more natural, & not overly made up
She wasn't allowed mascara at that age, as its more likely to go wrong when getting ready in a hurry for school. She does have long dark eyebrows though, so dint really need it or eyebrow pencil - if your DD is fair, maybe a compromise would be having her eyelashes & eyebrows dyed