Welcome!

I do not live in DFW metro area but knows people from the area. Plano ISD has decent gifted program called PACE. Many schools in Texas have early registration for Pre-Kinder but only for low income and military families.

Your best bet is to enroll your DD when she is 5 and take credit by exam when you register (you may do it before the school starts) and start from 1st Grade or 2nd.
http://www.pisd.edu/parents/assessment.accountability/CBEKN.shtml

My DD went that route and starts in 1st grade. She was still miserable until we moved to a different school with better TAG program.

Testing WPPSI-IV and WIAT-III may open door for other resources like DYS program (if she qualifies). Texas local group is awesome!