We are usually a very close family and hardly ever argue so I'm finding it difficult to know what to do. Every year I spend Christmas at my sister's house with DD, my parents and my sister. Our only other family is my lovely aunt (mum's sister) her husband and their 12 year old. Aunt lives too far to travel to us on Christmas Day, and Dsis doesn't really have space for everyone, so aunt always invites us all over a few days before for a family Christmas celebration. She goes to loads of effort, makes a huge traditional Christmas meal, bakes cakes, buys us all lovely presents etc - really goes to town.
Anyway, this was due to happen on Sunday. We'd all been looking forward to it for weeks, especially the kids. On Sunday morning, just as we were about to leave, we got a text from mum saying she was tired and had a bit of a cold so she and dad weren't coming. She hadn't even let my aunt know yet. Dsis and I were so disappointed. We knew aunt would've gone to so much trouble, and this would be her only chance to see family over Christmas. My mum has a history of letting aunt down and making no effort with her only neice. We were really embarrassed that they'd be so selfish and really upset on aunt and cousin's behalf.
Anyway, the rest of us went and had a fantastic day but it was clear that aunt was really hurt by the fact that they'd cancelled at the last minute.
When we got home late that night, Dsis and I both had a text from mum saying 'well thanks for the phone call!' She was annoyed that we hadn't called her during the day and that she'd been left out! Even though she was the one who'd cancelled. So I called her on it and told her that we hadn't called because we'd been putting all our effort into trying to make sure aunt and cousin had a good day to make up for the fact that they'd cancelled the only family Christmas we have for such a shit reason.
Mum was very offended and demanded an apology which I have refused to give (I didn't say anything nasty or rude, or untrue so don't feel I have anything to apologise for.) So now she is not speaking to me, and we are all due to arrive at my sisters on Christmas Eve to spend the whole of Christmas together.
My Dsis completely agrees with me but is trying to stay out of it as her and mum don't have the best relationship anyway, and Dsis is worried she'll just make things worse.
So, my question is, have I been unreasonable? And where do we go from here? Any advice would be really appreciated.