Should I Be Concerned About Irregular Periods?

My 16 year daughter was diagnoised with Juvenile Dermatomyosits in Sept 2010. She had just had her first menstral cycle in July of 2010. Her periods are very irregular missing months and having very light to very heavy periods lasting 2 to 10 days. Should I be concerned? I took her to a gynecologist who told us not to worry about it.
She also has elevated liver enzymes and hypothyroidism.