Skin discoloration above knee- lamictal

My 16 year old has been taking lamictal for about 2 months.  The dosage has been gradually increased to 200 MG.  She has had a discoloration above her knee for about a month now, but today she told me it itches.  It isn't red, and is about the size of a woman's palm.  It really isn't circular.  It is a brownish/purple color...more brown than purple.  I know that Lamictal can lead to dangerous rashes.  All of the images I've researched are red and blistery.  Hers is flat.  Should I take her off the Lamictal or wait until the weekend is over and call her doctor?  Like I said, she's had this thing for over a month, but it just started to itch.