Ah, there's a conundrum that's been brought up. 2B would rather not lie to her creator, but with 9S here, there's a problem posed: 9S shouldn't find out about her true designation.

"Yes, I'm an android. I'm a combat model." 2B says after a moment of deliberation. There's more than one combat model, after all. It's simply a matter of how Rita chooses to interpret her silence before she spoke on if she wants to dig up more information.