I mean this isn't a hot take, but my personal nemesis for Diana is Circe. Big name, tons of back story, power house witch, morally complex yet just their to piss on Diana's happiness at times, trade mark looks IMO, and she's already in the big 3 villains in line for that role.
What are our definitions for being an arch-enemy? Because, it seems to vary a bit. I don't think Cheetah's origins even with adding the vices of greed and jealousy really make arch-enemy material. Important 100%, Diana is the kind of person to try her absolute damnness to try and help someone that was once her friend, but Barbara, despite some genuine moments of sympathy, deep down doesn't want it. I think at least. This doesn't mean she isn't a threat physically, after all there are a bunch of supervillains that aren't nemesis material that can slap around the best of them.