I've been thinking about this case once more.
What is so bad for the GF about this deal:
"I'll buy you a ticket, but when I get an upgrade I will take it."
The alternative could be:
"You buy your own ticket, and when I get upgraded I will give it to you."
HTB.
According to the story posted in the OP, the exchange has nothing to do with who provided the ticket but the fact that the BF (in this case) was an FF'er and therefore deserved the upgrade.