What is considered "normal"?

My daughter(9.5yrs) just saw her pediatrician on Friday(8/9), she is 4'7" tall and weighs 58lbs. 2ozs. The paper(visit summary) that I was given at the end of the appointment says that her BMI is 13.51(2.57%). She was diagnosed with microcephaly as an infant. Is this "normal" for a child with microcephaly?

*Pediatrician was not concerned about her BMI.