"Hi dad, this is Bella, she's my teacher and I thought it'd be cool to bring her home with me"
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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).