By this age, they tend to be getting pretty specific about the mediums they like to work in. Does she have a particular medium she prefers for her drawing - pencil, charcoal, ink, marker, pastels? Painting-wise, does she use only watercolors, or does she use other paints as well? What she likes to use really influences the supplies you would want to buy. Things like the texture of paper you want for charcoal can be very different than what you want for marker, etc.
(Coming from first hand experience of having DD21 who is very artistic - but I'm not so I had to learn all of this the hard way LOL)