My neice stayed with my for 3 months while she found her feet in a new (and very expensive city). The deal was that she would help out with my two LOs around work. My birthday is on Xmas eve and I asked her whether it was ok to babysit then as I wanted to go to the theatre. She said ok and I booked. Just for context we never do anything on Xmas eve/we are not culturally Christian so it didn't strike me as this was in anyway unreasonable.
Fast-forward 3 months and my neice has now moved out and found her own place. I went to lunch with her and asked if she was still good for babysitting on that day. She looked at me blankly before saying in a very casual manner that she had forgotten and was actually going to spend that day at home in her home city as she had a few days off. First I heard of it and her tone wasn't apologetic.
I mentioned this to her mum (my sister) and said that while I understand my niece's plans have changed would it be possible for her to try and sell the non-refundable/exchangeable tickets as I'd only bought them as she'd agreed to babysit and there wasn't any other feasible childcare options which weren't a faff. The tickets were £200 by the way and I just don't want the hassle of trying to shift them.
Her mum said that she thought I was being unreasonable as her daughter had felt "pressurized" to say yes as she was living with me (news to me as she made herself at home while living with us (borrowing personal items without asking etc, not feeling the need to buy groceries etc, which was fine but hardly the behavior of someone who feels obliged by their circumstances) and is very good at saying "no" in general. She also said she thought it was unreasonable for me to ask her to babysit on Xmas eve (even though we never celebrate Xmas eve as a family and it was my bday). She said she would buy the tickets from me as otherwise I would "go on about it forever".
Am I right to feel annoyed at my sister? Although she's offered to pay for the tickets, her tone was very off and like I had been v unreasonable. My neice is not a child by the way, she is well into her mid-20s.