Well OP, leaving lights on- although unnecessary- doesn't actually use very much energy, especially now that bulbs are low energy.
As for your grandma, it depends what kind of heating she has and how well her house is insulated as to how high her emissions are.
I really dislike the implication that you have to suffer in order to live responsibly as far as climate change is concerned. It's possible to have low emissions and still be warm and toasty if you have a well insulated house and electric heating, preferably a heat pump. In fact, every year it becomes more eco friendly to run electric heating as the share of our energy generated by renewable means increases. But not everyone can achieve this without help.
There are those out there who like to rubbish that idea- the gas boiler industry has put quite a lot of money into generating negative publicity against heat pumps, for example!
I realise I've written several paragraphs, which I suppose is why people switch off- it's a complex subject and requires a lot of thought and research, while "common sense" climate denial one liners are spoon-fed to the public constantly by a well funded lobbying industry.
Probably in the time it took to write this another 10 posts will have landed regurgitating the same crashing, easily debunked fallacies again and again....🙄