Rush of recognition, flashes of memories she's not seen before (probably because they're not about either Nimue or Arthur) and she beams, shaking her head gleefully.
"Of course you are! Forgive me for not seeing it before; my head's full of... well, that doesn't matter. The important thing is that you're back. And so's Arthur. So!" She's about to launch into filling him in, but it occurs to her that she should probably confirm who she is, because if Arthur wouldn't have believed it if he hadn't known... She extends a hand. "Merlin, by the way"