Onset of Muscular Dystrophy in Children + CK Levels

Two months ago, my 3 y/o was complaining of upper left leg pain, thigh area. She was limping quite a bit. She also had a cold at the time. I took her in to PCP. They tested her for strep, neg., thinking leg pain can sometimes come from strep in young children. The pain went away, and is now back 2 months later. Blood work has been done which showed a slightly elevated CK level. My MD says a level of 135 and below is normal. My daughters is 142. My MD says he is not worried because Muscular Dystrophy PT's that he has, have CK levels in the 10's of thousands. He says her CK level could be slightly elevated due to her muscles reacting to blood draw or possibly injury. She will be seeing an ortho. MD next week. My question is, when children first show symptoms between 2 and 6 years, is there CK level already high? 10's of thousands, or does it slowly go up during the first years.? Are they born with high levels? or due they develope them. MD says he won't test for it again unless she shows more signs and symptoms. I'm scared. Any input would be appreciated.