WW has a Giganta, a serial offender, cornered in an isolated area, has control over the fight but stops because the criminal says she's not planning anything *at the moment*.
Despite the fact that, ya know, she should be in jail. Even if she's not The Joker, she is a killer and a brawl anywhere else would be exceptionally dangerous.
Hopefully, Diana just gives her time to part peacefully with her date, and then takes her in. Allowing her to get away, IMO, would be just stupid.