OP-sorry, didn´t sound very sympathetic & it does sound awful for you.
And just re-read & see you put "infrequent phone calls in OP"
And yes knowing it will happen doesn´t make it easier.
My Mum was nothing like yours at all in fact there´s only one event I remember.
2days before my wedding my sister said she couldn´t come so I was down a bridesmaid & therefore the flower girl as her daughter (4, only grandchild) also wouldn´t be coming.
I was gutted-2 days before & my sister chose work over my wedding.
Mum not sympathetic at all, more concerned at not seeing granddaughter-they were abroad & visits not that often.
She took the view that I was still getting married, but her lost visit couldn´t be replaced.
Even though had I not been getting married there never would have been a visit iyswim.
Unbelievable-never known her so selfish & was completely out of the blue.