Chanel 5 EDT, EDP and extrait are all slightly different formulations that smell slightly different. I'd ask your mother whether she still loves it, and if yes, buy the same strength.
The Bellasugar article is wildly off the mark, clearly written by someone who doesn't know a lot about perfume. To me, No 5 and Shalimar are polar opposites - the common factor is that both are very old.
I'd replace No 5 with another classic aldehydic (Arpege, Caleche, No 22, Guerlain's Vega etc), but agree that a blind-bought gift usually won't work. Some ELs have a similar vibe but many perfumes are love-hate because people have highly individual olfactory preferences.
The old rule that EDP lasts longer is wildly inaccurate too - it varies by perfume and your skin type. Ch 5 actually has a formulation meant for spraying your hair - spraying on cloth or hair is a good way to extend the lifecycle of a perfume.
Lidl have a dirt-cheap but decent Ch 5 knock-off, perhaps worth sampling.