She is Mexican and Caucasian.

She is quoted saying;

I grew up in a house filled with music. My mother, who is of Mexican and Spanish descent, used to sing to my English-Irish father, and between the two of them I was introduced to a diverse array of music…

Source:

http://www.lyndacarter.com/lyndaherstory.html

Her daughter Jessica Altman

  

After entering a local beauty pageant, Lynda Carter went on to win the title of Miss USA in 1973. Shortly afterward, Hollywood came knocking. Carter studied acting in New York and began making guest appearances on such TV shows as Starsky and Hutch. But it was her marquis role as Wonder Woman in 1975 that made her a recognizable star and kept her in the public eye for the years.

  
Lynda Carter with body double and the second pic is her on the show, hiding her identity behind glasses just like super man. Looks like theirs a trend among super heroes?