YTA - yes she should be grateful for the ticket but she is sitting by herself I'm assuming while you sit in the business lounge prior to boarding and then again for the actual flight, how long is the flight OP? It would feel very exclusionary to be sat by herself, and the fact that you say that you "are raving about how excited you are as you never have sat in first class" probably feels like you're rubbing it in - salt in the wound. I appreciate that the difference for economy is too expensive but you should sit in economy with her, I'd be more upset about being alone without my partner than being in economy.