Yes, the rash can be a serious reaction that signals Stevens-Johnson syndrome, which as I recall is a sort of autoimmune disorder that can be miserable and even lead to death.

Now that I've scared you half out of your wits (sorry!), let me reassure you that this is relatively rare. Statistically, about 10% of patients on Lamictal develop a rash, but only a fraction of them go on to develop full-blown SJS. Still, the rash IS a risk for which you and your daughter should be vigilant about monitoring her skin regularly, especially while she's ramping up her dosage.

Of course, any further questions should be answered by a pharmacist or your daughter's pdoc, but Lamictal is generally well-tolerated with minimal risk of weight gain and other less desirable side effects of bipolar medications. It does make the mouth pretty dry, and it tends to make one a little drowsy during the day, but it's not anything that can't be overcome.

FWIW, I started Lamictal about a month ago and it has been nothing short of miraculous for me---I was a train wreck when I first started taking it, but after ramping up a couple of times already, I'm feeling almost like my 'normal' self again. I hope your daughter finds the same kind of success with this drug that I've had.