I wouldn't worry too much about the memory, as long as it's at least 2Gb, you can always upgrade later at a relatively low cost. If budget is limited at the moment, then I'd focus more on the things like the processor type and speed that aren't realistically upgradeable. Other things that aren't upgradeable so need to be decided day one include screen size, weight, look/feel, battery life, etc.
Pretty much any new laptop on the market will run Office happily enough. Everyday web browsing doesn't need a powerful machine either, nor does looking at or storing photos (although she might want a big-ish hard drive if she has thousands of them). A bigger screen might be nicer to look at them on though. Photo, or more importantly, video editing will need a more powerful machine. Games will need a more powerful machine. If she's going to have lots of documents open and copies and pastes between them all (if she's an Excel mad accountant or something!), while streaming half a dozen You Tube Videos at the same time, then she might need to look at a higher spec machine. If she doesn't do any of these things then the cash is probably better spent on the ergonomics,,,like a slightly bigger/better screen, or a slightly lighter one if she's going to be carrying it about, or a better feel to the keyboard, etc. Also, if it's going to be sitting out on public view at home...how does it look?? Does it fit in with the rest of the decor?? You might laugh, but we all oooh and aaaah over hi-fi pics here, so it is important to some people! If looks are important, and all she is using it for is the things you've listed then I wouldn't worry too much about a certain processor being 3% faster in a bench test than another one, etc. It'll make very little difference to her real life experience
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