Elevated Platelet Count

My 16 year old daughter's blood test 2 months ago revealed a platelet count of 437,000. All other values were normal. Her primary care physician did not report this to me, I found out myself when I called for her blood results. My daughter was not taking medication at the time.

About 2 1/2 weeks ago, my daughter was started on 600 mg. Of neurontin for a mood disorder. The other day I noticed 3 good sized bruises on her leg. She remembered banging her leg the other day but stated that 1 of the bruises was there before she banged her leg.

I asked her psychiatrist if the neurontin could be causing these bruises. She said unlikely but not impossible so I am having her blood work redone (platelet count, liver function, etc.).

My question is what could be causing the elevated platelet count 2 months ago? Could the bruising be a sign that the platelets are either rising or dropping? I am very worried. Does this sound dangerous? Are there other non-disease things that could cause the platelets to be elevated?

Thank you.