The previous reply you got from Dingleeire is right on. We're all afraid of these medications, but I can't stress enough how much worse it is to let this disease rage out of control. You don't want the disease to be doing serious damage.
Hopefully as you indicated, your Daughter is on the mild side, and her symptoms will be well controlled. You will get alot of differing opinions on Pentasa. Some will tell you that it has worked well for them. Most GI's don't prescribe it anymore, as they don't feel it is an effective treatment.
I'm not trying to suggest that I know for sure that it doesn't work, just trying to inform you that you should get more opinions on Pentasa before relying on it alone.
THe step up to 6mp or imuran is a logical one. Good luck with your decisions, be informed, do the best you can, and your Daughter will stay way ahead of this disease, and live a normal life.