Laptop recommendations for my mum?

Does anybody have any laptop recommendations for somebody who is not computer savvy? She will be using it mostly for Microsoft office related tasks; Excel, Word, etc, but has said her priority is that it be easy to use and mobile, but also with good reliability, battery life, and a large screen.

I should add, on the large screen point, that she is 70 now and due to have cataract surgery in December, so screen size may be less of a pronounced issue after that time (hopefully). I have been searching for good Laptop ideas, but I’m unsure which laptop will best suit her specific needs. I was looking at the Dell XPS15, but the reliability issues I have read about have completely put me off.

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1. Total budget and country of purchase:   
£1,500, UK.
2. Do you prefer a 2 in 1 form factor, good battery life or best specifications for the money?  
Best of all worlds??  She needs eliability and mobility primarily, but screen size and performance matter also. 
3. How important is weight and thinness to you?   
Mobility is important as she is buying to move away from desktop, fixed working locations 
4. Which OS do you require? Windows, Mac, Chrome OS, Linux?   
Windows is preferred, but open to anything user friendly.  
5. Do you have a preferred screen size? If indifferent, put N/A?    
Difficult to say as the situation now will hopefully change post her cataracts surgery.  As of now i was hoping at least 15 inches. 
6. Are you doing any CAD/video editing/photo editing/gaming? List which programs/games you desire to run?  No, she's mostly internet, MS Office applications (Word, Outlook and Excel mostly)oriented.   
7. If you're gaming, do you have certain games you want to play? At what settings and FPS do you want?    
Not applicable   
8. Any specific requirements such as good keyboard, reliable build quality, touch-screen, finger-print reader, optical drive or good input devices (keyboard/touchpad)? 
I think a backlit keyboard would be good for her, but reliability is very important (as always i guess).   
9. She needs a mobile, reliable laptop first and foremost. Ideally it will be something that looks nice, is user friendly, mobile, but can also handle long hours of Microsoft Office use without overheating. If it can be 15 inches then even better.