Chalk isn't made in sterile places so I highly recommend against eating it. Though it may seem safe enough, the places it is mad could have left all sorts in it. It may not be massivly dangerous, but you never know. You should try to prevent your friend eating things that are not made to be edible.
It's made of calcium sulfate which is harmless as that's naturally found in tofu and some dark green veges. Perhaps there are other compounds added to it but calcium sulfate is the main one, so it may be healthy as a calcium supplement in an odd form LOL.
The only damage may be from its brittle nature to the mouth and digestive system. Depending on how much she eats, although I doubt this, she could develop hypercalcemia, which can be life-threatening. The way I learned to remember the main symptoms of hypercalcemia are from this mneumonic: groans, moans, bones, stones and overtones. In other words, constipation, depression, fatigue and possibly kidney stones. Other symptoms can be anorexia, nausea and vomiting which may help her in making her not want to eat chalk.
I can rip you off, and steal all your cash, suckerpunch you in the face, stand back and laugh. Leave you stranded as fast as a heart-attack.
- Danko Jones (I Think Bad Thoughts)