I have a 8 and a 6 Plus. The 8 shoots more pixels so zooming in looks better. Side by side when I take the same shot with the 8 & 6 Plus, the 8 looks a bit nicer. It's not jaw dropping better, but when you compare them side by side, the 8 often looks a -little- better.
I just take fast snapshots anyway. Super high quality isn't important to me. I usually delete my pictures after a few months when I get bored of them -so quality isn't that important.
(and that's coming from an ex- pro photographer). I see all iPhones as point & shoot convenience cameras.
I've owned a single lens (used on a pro camera) that cost way more than the most expensive iPhone. I've lost interest in high quality photos. A snapshot is good enough for me to jog a memory.
I have to agree with @MarkX some more info would be needed to give an honest opinion. Strictly based on the camera, I'd choose the Plus, for the zoom lens, but there may be other factors in your decision.
Go for the 11 unless she’s on a strict budget. The 8+ is acceptable, but it’s been left in the dust by the newer phones. An 11 would last her another 4 years or so. Day to day usage is similar on both, but the 8+ camera is several steps below the 11.
Everyone is different. For me the iPhone 8 Plus display is better for reading than the iPhone 11. The iPhone 8 Plus has a higher resolution display and the default text size is larger. These two qualities taken together result in sharper text that is easier to read for those who don’t have perfect vision. The iPhone 8 Plus display is also wider than the iPhone 11. This is an advantage if you play board games like chess because the chess board, which is square, will be larger than on a phone with a narrower display, no matter how tall it is. Of course, the iPhone 11 is a better phone in most other ways. It just depends on what is most important to you.
Don't sleep on the 8 Plus. It was an absolute beast when it was released and it still is to this day. It's basically an iPhone X in a classic iPhone chassis. Super solid, handles iOS 13 without breaking a sweat, great display, wireless charging, stereo speakers, etc etc etc. Not to mention it's quite a bit thinner than the 11.