OP here. My understanding is that Jessica was intending to fund her share of the beach house herself, and make her own travel arrangements to and from the coast.
To be clear, I was one of the people who advocated for letting Jessica spend Christmas at the beach house. The main reason for this, was that (as another poster said) John's Christmas Day traditions sound pretty dull and stifling! (Not that I told John this!). But I also feel that Jessica is a legal adult and old enough to choose for herself where she wants to spend Christmas.
That said, I can completely see where John is coming from - I'm not a parent, but "letting go" must sting sometimes. I guess there's always the fear that if you "let them go", they won't ever come back? John also said that these days, his family doesn't actually get to spend much time together. Between work, uni, school, sports, and other schedules, the four members of his family are always in and out. Plus, Jessica socialises a lot with her friends and boyfriend anyway (she sees him nearly every day as it is), so I think he was looking forward to his family spending some quality time together.
Also, John might be feeling a bit down, as he lost a parent earlier this year. Said parent lived 3 hours away, so they didn't spend Christmas Day together, but they'd normally catch up in the week beforehand. This was John's first Christmas without his parent, so it might have been extra-tough for him.