I feel that every big-name hero sould have at least one villain who goes through a redemtion arc that sticks.

Yes! Does Selina Kyle count?

This is especially true for Diana, who is empathy and persuasion more than anyone else. She should have at least a couple that stick and I guess she's already got one that hasn't in Silver Swan. Definitely not Minerva. But I have someone in mind for Diana to convince to permanently switch teams... uh, so to speak.