Two book recommendations for you:
Living With Intensity: Understanding the Sensitivity, Excitability, and the Emotional Development of Gifted Children, Adolescents, and Adults, Susan Daniels and Michael M. Piechowski (editors)
5 Levels of Gifted: School Issues and Educational Options by Deborah Ruf
I'd hold off on the testing for a couple of years unless I had a specific need for it. Testing results tend to be more stable around the age of eight or so. The Ruf book has plenty of anecdotal evidence from early childhood reported by the parents of gifted children. A Level of Giftedness (from the 5) will probably be as helpful as an IQ score in planning the next steps for your daughter.
