Capitalism convinces too many people that working is the only thing of any value. Why would not working be ‘monotonous’? There’s a huge world of things to do out there, aside from paid work!
This! If you woke me up on any given day and said, today is yours, you can spend it doing anything you like, what would I choose to do?
Creative projects, seeing friends, relaxing, reading, watching TV, going to an exhibition or a museum, walking in a beautiful park, out for a nice lunch... the list goes on and on! "Go to work" would come QUITE far down the list. I don't think I'm unusual.
Then just imagine that, having that choice every day, and I think that's what it would be like! Bliss!
There are also loads of really rewarding and challenging volunteer roles available, if you still wanted to do something of service, in mental health, education, children's welfare and extracurricular clubs etc etc. In time, perhaps some grandchildren to be with.
It's great that you find your job so fulfilling OP, but I'm sure you can imagine that other people can think of lots of other things they'd rather be doing with their time. It's really nothing to worry about for your friend. Presumably she has had the choice to work outside the home and hasn't felt called to do so.