M.L.
I'm a hairstylist and I have a chi. Paul Mitchell has a great one as well, (it may even be better than my chi).
( I usually am against frequent flat iron usage, but I just got a haircut that requires I flat iron my hair, not happy about it!)
If she uses a good heat sealer, like Paul Mitchell's Seal n Shine or any type of thermal protectant spray while she's ironing, and if she uses thin sections and combs it as she irons, then it wouldn't take as long or tug/damage her hair... but yes, on the cheaper versions, having to repeatedly iron will be more difficult and damaging.
Sometimes, you can find them for cheaper on ebay. ALSO, she's 18.. at that age, I had to buy my own stuff like that.