Not a discussion, she's just happy going with me and knows it was A) a difficult ticket to get and B) it was something that I got before we met.
If I had bought that ticket with her in mind, sure it wouldn't be an issue. We're actually doing a lot of things together and I'm including her in a lot of my plans that are usually solo things.
Having a girlfriend that really likes you and is happy to spend time with you enjoying a common interest is awesome. She won't get hung up on not sitting next to me, trust me.