"Hi dad, this is Bella, she's my teacher and I thought it'd be cool to bring her home with me"
Fr though, something along the lines of "This is Bella, she's my friend and she was going to spend Christmas alone so I brought her home to spend it with us, I hope you don't mind."
I think this is a pretty agreeable and plausible scenario, Neil being the awesome dude he is would probably be chuffed. Seen identical stuff like this happen IRL a couple of times as well (not as in bringing you secret gf home, but bringing a friend home to spend Christmas or New Year since they would be alone otherwise).