QFT. (And I don't think I've ever used that abbrevation before! )
They retconned an origin for Donna (a pretty good one) and more or less suggested she was "Diana's sidekick," in much the same way the other O5 Titans were sidekicks to their mentors. But they never backed it up with stories, current or flashbacks. She didn't appear in Wonder Woman's comics. She wasn't living with Diana Prince - or, as far as I could tell, anyone at all. She was more an idea of a character situated in the DCU like Robin, Kid Flash, Aqualad, and Speedy were - but not actually a fleshed-out character, even to the extent they were (which, admittedly, was variable). This may be one of the reasons it was so easy for them to just completely revamp her origin and severe her ties to Diana, Hippolyta, and the Amazons. (Much like they just decided Wonder Woman was no longer a founder of the Justice League.) But, like you, I don't think that was a good thing for the character. And it set the precedent of, "well, we can just make up whatever we want to about where she came from and even what she is, over and over again."
I think that's a question of when you want Diana to first come to Man's World and start her career as Wonder Woman, relative to when Superman and Batman start out. You'll get a lot of opinions on that. And I'm not sure that what works in the movies necessarily works in the comics.I was fine with Wonder Woman having a long career--long enough to have saved the child from the fire--because as an Amazon she could have been around for a long time. And I think the continuity was fuzzy about when Steve Trevor crashed on Paradise Island--the updated version would have had him crashing during the Korean War. Which would still give Wonder Woman more than twenty years in the star-spangles.
This was also when the Weisinger comics said that Superman had first appeared in 1938. The attitude towards time was different back then, before DC copied the Marvel approach to time.
The current comics should copy the popular version from the movie. Diana should be very old yet look young. And Donna should have grown up with Diana as a mentor and a role model.