totally depends on the unit. I've been to ones where pencils were allowed, and markers, but not pens (not sure the logic, because markers were plastic also). If you send her either a sketchbook or coloring book, most places will not allow spiral-bound or things that are stapled. the pencil crayons that don;t have the wood around them will probablly be ok, as might chalk . Crayons might be ok. Paint generally isn't as they want to make sure that it's not ingested, though if you get kid-safe non-toxic stuff it may be ok. Some places will hold the art supplies until she can be supervised using them. Other places are sticklers.
It's awesome that you are doing this. I know it was always nice to have my own art stuff with me. <3