"Hi dad, this is Bella, she's my teacher and I thought it'd be cool to bring her home with me"
![Kappa :Kappa: :Kappa:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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).