@LordMomo - a quick Google search brings up mostly what I expected- that chalk is non-toxic and doesn't cause any long term problems. But there's a couple of isolated case reports of chalk-induced pulmonary fibrosis - that is, severe scarring in the lungs. Pulmonary fibrosis has about a five year life expectancy without lung transplant.
So short answer- not much, unless you want her to be really unfortunate.
You can consider for instance also having her be an asthmatic whose asthma can be triggered by dust in general.
Other than respiratory issues, and maybe some eye dryness, I can't anticipate it causing other problems. If she has sensitive skin (and especially if she is asthmatic) it may cause eczema or dermatitis but in general it's not an irritant.
Cool concept though!
