[Maybe choosing it is the difference between what makes a kiss real or not. After all, their first kiss was inside one of those traps set up by the mistletoe bots. Maybe it doesn't matter if their bodies were there for the second kiss or not. They wanted it, and so it was real. In the end they'll have to define their own reality especially if they can't find the conclusive answers.
But for now she isn't defining reality so much as embracing this kiss—this connection with him by responding in kind to the deepening.]