Alyssa Searrs from Mai-HiME. She may not have the ability to call down an orbital strike anymore(Artemis was a fake Child, so probably didn't return when Miyu blew up the pillars) but Miyu's still a kick-ass battle android who looks a lot like an older Rei, and I can imagine Gendo ordering Ritsuko to check to make sure all the pickled clones are accounted for the first time he sees a surveillance photo of her.
Alternatively, Nao Yuuki, also from Mai-HiME. Imagine a Rei who's willing to put the moves on Shinji.
Better yet, Haruka Suzushiro from Mai-HiME as well. With Haruka for a guardian, Rei would have no choice but to be far more outspoken, not to mention have a habit of mispronouncing and misspelling words, having "learned" by listening to Haruka speak. I can also imagine Rei calling Asuka "annoying bubuzuke girl" Which is close to what Haruka usually called her rival Shizuru(well, Haruka considered Shizuru her rival, but I doubt Shizuru felt the same way, she wasn't the type to think in such a confrontational manner... well, except for that time she went nuts and went on a rampage which left the First Division in ruins)