LOTR, she's not going to be any actual help at any point. She won't want to be. She will want to have photos and be able to tell her friends she has a great relationship with her incredible talented, beautiful GC! So send her photos and never, ever let her know about any struggles the children have.
In terms of teaching the DC strategies, I mean as simple as:
Visiting at Christmas, presents given- on the way remind them to say 'thank you, that's really kind' even if it isn't something you want (an electric toothbrush when you are ten, a pair of too small, grandad style slippers when you are 14, a fluffy pink biro when you are an 8 yr old boy).
When you eat at their house, tell DC that they only need to behave politely at the table- you have brought plenty of snacks they can eat if they are hungry after dinner.
Before grandma arrives, remind them she may talk a lot (doesn't stop talking the entire time) but it's ok, they just need to sit in the room, smile occasionally, and can go on their games gadgets/read a book).
Basically I ran interference between them and her, made sure their needs were quietly met with no need to involve my mother, and arranged things so both were comfortable.
As they got older, coach them on things they can tell her about- swimming lessons, party last week, friend's new dog etc.
In a way, it's old fashioned manners- but she gives no quarter while a child learns those skills, so you prime the kids for success. Teach them phrases to say that she will like to hear 'hello grandma, you look really well is that a new dress/was your journey ok/did you have a nice holiday?'
Does that make any sense? She's never been nasty to my children- incredibly thoughtless, yes, greedy and selfish, yes- actively nasty, no. She wants to keep them on side.
They are incredibly patient with her, and recognise she's a little old lady who is useless at relationships and struggles to get people to care about her because she's not likeable.
They also recognise that she actually has no skill, no resource, she simply doesn't understand why her relationships are not like those of other people. Her friend is very close with her own DC. Mum complains they are all in each other's pockets and should be more independent, yet also complains because we don't take her on outings/on holiday/out for a meal/on girly shopping trips. She doesn't enjoy being with people, she just wants people with her because it's not nice being on your own and she needs an audience. She has no interest in whether you are enjoying yourself or not.