OMG - I am sooo lucky and I didn't even realise it till now! My mum will only ever offer great foods - no alternatives.
I was such a horrible and picky eater that I think she is determined to have another go with her grandchildren.

I used to make quite a fuss - 'oh you grown up girl, you tried onions', that dd started making a point of knocking back crappy foods if offered because she loved the praise so much. However she was a little older (about 5-6) when she made these decisions, and if she felt ill after some foods (I hear you on the nightmare issue Dach) I pointed out that it may well be the chemicals in the chips that could have done it even when she was little. Her tummy was pretty sensitive and she noticed the effects and put two and two together.

With your mum, maybe you can mention the nightmares to her - "I really think it might be the xxxx they had the other day", we are going to cut that out of their diet and see how it goes".

Nannas tend to go by the "well it didn't hurt you/me/your sister" etc, but they seem to forget they/we weren't eating half the crud on offer these days.

Aldi eeewwww.