It's the journey, the transport. None of you will have a great time on that flight . You will sleep, uncomfortably, read, plug yourselves into a series of movies and count down the hours.
Also, the likelihood is that the seating wil be 3-4-3 and so unless 4 of you chose a middle row (God, why would you do that?£ one person would be on their own anyway.
On a flight of that length I would try and bags you each a window seat rather than be in the same row, though some prefer aisle seats. Doing the best for individual comfort is more important than sitting together.
If you think she will want to continue an exclusive first class lifestyle that the rest of you can't afford when you get there , then that will be much more of a problem . But presumably if she did that kind of thing, you wouldn't a be friends?
At this stage if you cause an atmosphere over this , it will be as much your doing as hers. I would be gracious, say 'you lucky thing ' and not snipe or nurture resentment .
Apart from anything else you will
just look jealous. (I would be so envious! )