Mums table manners are so bad

[Brunomars65]

My mums table manners are awful, eating whilst talking with her mouth open constantly.
Sometimes she'll end up spitting food at other people eating with her because of how much food is in her mouth while she's talking and its so embarrassing. Its got to the point where I dont enjoy having meals with her as much, especially in restaurants. Its so offputting when I'm eating my meal and can see all of her chewed food in her mouth while she talks to me.
She went on a date for the first time in a long time recently so I tried to subtly hint at it saying "okay so remember good table manners, no talking with your mouth full etc"
Both me and my brother have said to her in the moment to finish what you're eating/can't understand what you're saying because your mouth is full.
She wants to invite my friend for dinner at hers but I am hesitant to because its so embarrassing.
I think I'm just going to have to have a straight conversation with her but she is very difficult with perceived criticism and I think it'll probably turn into an argument.
Any advice please? She is totally compos mentis by the way, in her 70s no medical problems. She's always been bad for it but feels like its got worse.

She won’t change now

My mum cuts up all her food into teeny pieces. Like the whole plate at once. So you give her a steak and she will hack the whole steak up into tiny bits and the potatoes and the veg and finally shovel the whole thing in.

It’s not because there is something wrong with her. Like as in, she has problems eating. She’s eaten like that as long as I can remember. Lord knows where the hell I learned table manners. It wasn’t at home. I went to private school and I suspect it was watching posh friends eat. I somehow learned how to use a knife and fork like a normal person who doesn’t eat like a toddler, thank god.

As for this dinner invitation, she isn’t going to suddenly eat properly. I think you decline on behalf of your friend. Or you warn your friend in advance and make a bit of a joke about it.

How bizarre. Surely in her 70 years on this earth someone has pulled her up for eating like a pig at a trough? Your father? How did/does he cope?
My husband can be somewhat devoid of table manners if left to his own devices but I have pulled him up plenty of times especially in front of the children (they now have lovely table manners!), in my husbands case he grew up in an atmosphere where you shovelled food down asap or someone else would eat it and it is a seemingly hard habit to break.
She won't change now, especially if she is thick skinned enough to have got to 70 without realising other people don't eat like that. I would just decline the invite on your friend's behalf and change the subject if it is brought up again.