Xaltd1, I am partially impartial. In that I have a mother that really just isn't very enjoyable to be around. I had a bad childhood, but my mother never misses a chance to compete with me in anything. When it's bad "I had it worst". When it's good "I did it better". She told my husband various odd things you would never expect a mother to say, like I would manipulate him or that I would make things up? I didn't find out she said some of these things until years later when I got annoyed at my husband for disliking my mother so much. After finding out more about who she really within the last couple of years, I don't blame him. She's said some pretty unmotherly things, and he's said after 8 years of marriage I am nothing like some of the things she's said. It's funny, because she does these things, but then other times acts like the world's best mom (talk about mind games)
I tell you this because I understand what it's like to have a mother that seems to want to see you feel bad about yourself.
So here's my take on this....
It is quite possible that Anna did not word herself at all how your mother said. The conversation could have gone like "my daughter wants to know if she can come to the party" "oh? I didn't send her an invitation? huh... well sure, she can came" and your mother calls up with a quick "she said it's ok if you come" as though it's something that really didn't matter to you.
It's only a possibility. If you are feeling hurt by it, I wouldn't jump to the conclusion that Anna was being shallow, but maybe that your mother just really sucks at her people skills. There's also the possibility that her son asked for Anna's address book or something like that and he sent the invitations himself, but he didn't realize you are that close to his mom or that she always goes to your birthday dinners?
Though, honestly, I wouldn't put too much weight on the words of a mother that is difficult to be around. I'm still trying to learn not to let my mother bother me, and I still need to vent sometimes, but in the end, it really isn't worth it. I'm sure you already have stress from other situations in life, letting your mother get you down is just like self mutilation. Just remember when she's being a judgmental sour puss that it's not because there's something wrong with YOU, she probably has some psychological issue burried that she feels the need to make you feel bad about yourself either through direct or indirect offensive speech.
She probably won't change at that age.... but then again, my granddad recently had a whole new turn around in his religious and moral perspective on some things, and he's pushing 80! Kill her with kindness, and you know what? Next time she points out a flaw.... I'd say "mom, I know you may not approve of who I am, but I do. I don't appreciate you picking at my flaws all the time. You're my mother and you're supposed to love me, not judge me"
I would let the birthday party thing slide. You just need to remember that a lot of people really just suck at social etiquette... then again... there's also her age. She may simply have forgotten or thought she already filled out an invitation to you (seriously, I'm doomed when I get older with things like that.... I already have a poor memory, lol)
Either way, it's really not worth stressing yourself over
Heck, next birthday, you should just do something different, forget the dinner... and fly out to see your son and have a good time!
You shouldn't be stuck dreading your birthday dinner. Have fun this coming birthday