I think Wonder "Girl" is a step backwards for this character. You wouldn't, for example, call Wally Kid Flash after being the Flash. I think the same is true for Donna Troy; Donna has taken up the mantle of Wonder Woman for a short time, so to be called WG after that seems weird.
As for codenames, besides Wonder Woman, I think Asteria would be a nice Titans of Myth tie-in. Fury is another name that should be considered, as that's Donna's Earth 2 counterpart name and has ties to Amazon history. I think that would fit Donna nicely by keeping her deep ties to the Amazons mythos while at the same time, establishing her as her own character without including "Wonder" in her names. Another option is Olympia, which was a failed attempt back in the 90's as a new codename for Donna. The costume was meh but, the codename wasn't bad for her Amazon/Olympian/Titans ties.