It won't happen. Even if any good choices existed, Romney doesn't want to have to spend the first week after selecting a running mate just explaining over and over again why he didn't pick another Sarah Palin, which is what he'd have to explain with any female running mate regardless of how similar to Palin she actually was.
Nikki Haley? Young, charismatic, a minority. She's said she wouldn't do it, but the cardinal rule of running for Vice President is to act like you're not running for VP.
And she's about to be indicted.