My mum needing a new cooker def started a pattern of not eating enough but agree with you and your gran that the gas has to go. Slow cooker, microwave and induction hob way forward. Induction hob she might get used to or not as new things are so tricky for our loved ones with alzheimers to get used to! Its such a shame that all the appliances get old and unsafe at the same time and the dread of replacing things for the PWD to struggle with is terrible.