If your child attends a private school or is homeschooled, you may need to pursue private testing for her. Contact your pediatrician about a referral to a child clinical psychologist or school psychologist in private practice in your city. Pediatric psychologists or child clinical psychologists on staff at medical centers or universities are also appropriate professionals to work with your child. Try to get at least three names of such professionals; then call each one and ask about their experience assessing gifted children. They should also be able to tell you in advance their schedule of fees. Some health insurance plans may cover the costs of such testing, but you should inquire in advance to be sure.
A helpful book you may want to read is Joan Franklin Smutny's Stand Up for Your Gifted Child. The chapter "Getting to Know Your Child's School" discusses the roles of various professionals in the school, how schools identify gifted students, what programs schools offer, and other relevant topics. Other chapters in the book deal with characteristics of the gifted, parental advocacy, and a host of other topics.