I totally agree with loulou. I had terrible acne all through my teens/twenties, tried every cream, tablet etc. Im 35 now and I started taking roaccutane about 6 years ago and have never looked back, I only wish I started them when I was in my teens. Again, like loulou, I get the odd spot when my periods due, but nothing compared to what I was like in my teens.
I was on a 12 month course and the only thing I could say that affected me was the very dry lips and hair and maybe a bit weepy now and again but these side effects only kicked in about 2-3 months after starting the tablets. Your daughter is only going to be on for 4 months so hopefully she shouldnt have too many side effects.
She will thank you in years to come, but both of you will not regret it, just keep an eye on her, but I am sure she will be fine and have the most beautiful skin next year!
If her face does start to get dry, try using Aqueous cream for face and body and Burts Bees lip balm. both very good.
Good luck to both of you x