Your sister is definitely not being unreasonable. Did you sit down and do the maths before forming your opinion?
Did you consider that pensions do not tend to increase in line with inflation?
That potentially she would be giving up 15 years of earnings and pension contributions on her current salary?
That she might live another 40 years?
That she'll find it difficult to get a job at her level at the moment?
That it's easier to get a new job when you're employed as opposed to unemployed?
That in London, £1000 a month before tax will just about cover her costs, leaving little for clothes, hair, travel, hobbies, courses etc?
I think your sister is being extremely sensible, and you should stop trying to persuade her to do something so utterly stupid.
And by the way, hardly anyone loves or even likes their job - they do it for the money.