I'd like some other views on this, as I freely admit to not always keeping things in proportion.
DP's brother lives in London, but always comes up for Christmas. This year, his gf is coming up between Christmas and New Year. 'MIL' has announced that she will be hosting a buffet for family while she is up. Invited are me, DP, DP's cousin and her husband and DP's aunt.
My mum moved down to the town we live in back in 2016. She now lives about a 20min walk from us and 'MIL'. No mention of her being invited. Now, for many years it was mum and me against the world so I do take things to heart on her behalf. She might not even want to come along, but it's the fact she hasn't even been invited. AIBU to be annoyed?