

In the current storyline of Donna Troy, as seen in Wonder Woman, she has lived a great number of lives, so we currently as readers do not know who she truly is. Is the young Wonder girl Donna Troy? Was Donna Troy Troia, then Darkstar? Was Donna Troy a goddess who defeated her son from an alternative time-line with the help of the Teen Titans from the future?
John Byrne destroyed the character of Donna Troy when he took on the challenge of Wonder Woman following issue #100. Specifically, John Byrne has to add his "touch" to each comic he works on. The "touch" on Wonder Woman was killing Diana off; bringing Hippolyta into the mantle of Wonder Woman; transforming Hippolyta into the Golden Age Wonder Woman; and revamping Donna Troy's origin. This idea destroyed years of work by Marv Wolfman and George Perez. Wizard Magazine had a few comments on John Byrne's Wonder Woman: read this.
Here are the origins of Donna Troy. Please read them to find out "Who is Donna Troy?!"
DC Digest 1980 reprint. Origin of Wonder Girl

The New Teen Titans No. 38. Origin of Donna Troy
The New Titans No. 55. Origin of the original Troia
Wonder Woman: Secret Files and Origins #2
Origin of Troia (Current Version 1999)