Help! Need inspiration on how to kill someone ;-)

[megrunning]

In my novel I need to kill off one of the characters and can't figure out how. She needs to be murdered by someone else, but its a mercy killing (sort of) and the death needs to be quite peaceful and needs to look like an accident or a natural death with no clues it was murder/suicide.

Other background is she's in her mid 40s, middle class and its summer. the death needs to take place at her home.

Carbon monoxide seems the best but not sure what appliance could be used and "faulty" in the summer.....Any ideas?!

Wet hands and dodgy light switch?

Some of these would lead to a gruesome end. it's quite hard to think of a mercy killing type one though.
Is the victim in on it? That might make a difference to the most suitable method.

Recently saw a programme exploring toxicity of uncooked kidney beans. Apparently a good handful could be enough to poison and kill you.

Maybe a friendly lunchtime catch-up in the garden and the culprit brings a bean salad, but doesn't eat it herself?!