As long as I'm on about the supporting cast of Wonder Woman, there's one female character I really wish they'd add to it.
Ystina from Seven Soldiers: Shining Knight.
Can you imagine the effect Diana would have on someone like her? She's a young woman from an ancient Celtic society who hid her gender in order to become a warrior. (I believe the Queen's shown in armor in a flashback, but with Ystina's actions I think that's a strangeness.) Diana is female warrior of incredible prowess from a society of female warriors.
Not only that, Diana is an honest-to-gods Princess (with really impressive gold armor) and Ystina's a knight without a liege. There's no reason someone of Arthurian values and virtues wouldn't imprint on Wonder Woman and pledge their sword to her forever. Can you imagine Ystina exclaiming that she sees the light of Camelot in Diana's words and actions, then dramatically kneeling and holding her sword up to Diana to offer it in her service? This is a scene just waiting to happen.
On Diana's side, she would certainly understand coming from a warrior culture and finding yourself adjusting to the 21st Century USA. She's experienced this sort of culture shock before. As a warrior from an idealistic monarchy she'd understand many of Ystina's expectations. (But not so many that we wouldn't have some interesting confusion and disagreement between the two.) She'd be a fine mentor in addition to a liegelady, and she'd be that much needed emotional support for Ystina.
Of course, that might just be my fixation on Arthurian legends imprinting on Wonder Woman. Hippolyta, to me, seems very much a King Arthur figure. She's a great warrior in a leadership position, and she varies in her morality and alignment according to whatever point the writer wants to make. Phillipus is clearly Sir Kay the Seneschal, but the badass one of the early Welsh stories rather than the guy who got unhorsed by everyone in the Mallory books. Diana's our questing prince/princess/knight. She's out righting wrongs and spreading the Queen's justice in the wild lawless lands.
Really, the pre-Crisis adventures read a bit like those old romances. (And not just with the strange attitude towards characterization and logic.) You have the Knight and the lady who needs his help in those. They travel for a while and he solves her problem, having adventures along the way. Steve Trevor's like the lady who starts the quest. His career in military intelligence makes him the center of all sorts of problems, especially during the war when he was in constant danger of spies seeking information, and he will either seek out help from the Princess of the Amazons or by lucky coincidence be found and rescued by her. He's not just someone who tags along to be protected, he's either the initiator or the object of the quest. Just like the damsel in the old stories, who often accompanied the questing knight like Steve accompanies Diana.
Hell, the Amazons actually had a tournament to decide who would get the honor to escort him home. And that's the one time I absolutely want them to establish he's awake on the island (I wasn't too happy with movie-Steve being so active on Themiscyra, it seemed off to me), during the Tournament. I want someone to do that scene with Steve sitting in a little chair (with his feet on that gold rug they used Pre-Crisis to avoid activating the curse) by Hippolyta's side, anxiously watching the tournament.
That's right, just like Guinevere.
Not only that, I want him to give Diana a scrap of parachute material or his tie to carry during the tournament like ladies gave knights their scarves or sleeves. Any writer who did this I would love forever.
Since they aged and put Steve aside, Diana's been kind of like Gawain. She often has an opposite-sex companion on her quests, and it's a different person every writer. The Knight errant impression is still very strong to me post-Crisis. That's probably the nature of superheroes, though. They're a modern continuation of the same idea as the old Arthurian romances.
Except I think it's a bit stronger with Diana than fully modern-world heroes, because she's a traveling princess from an enchanted land over the sea. A traveling princess who rescues dudes in distress. From an enchanted land where they have tournaments over who can escort a man home.
Yeah. Ystina could be comfortable in this franchise.