Does she use it on her lap, or on a desk. Essentially, there are 2 formats, those that have a numeric pad on the keyboard, larger screen, the touchpad offset left a bit. These tend to be heavier, more consumer orientated. The other is a bit smaller, no numeric pad, smaller screen, touchpad central, ignoring the very budget ones like Chromebooks, these tend to be budget business (in your pricerange).
I can't use the former on my lap, due to extra weight and the offset mouse.
So you need to sort that bit first.
Spec wise, forget AMD powered ones. Needs to be a minimum of an i3 CPU, worth spending a little extra on i5 if your budget will stretch. 4Gb RAM is fine for all general office application tasks and email and browsing, but may need more if using Photoshop or CAD type tools. Disk wise, I'd personally sacrifice disk space for an SSD. A 120Gb SSD is the absolute minimum really, and is comfortable enough for Windows, Office and so on. If you store all your photos and music, or do any video work, larger will be needed.
For the most part, if its sold in PC World, its junk, and will do well to outlive the warranty.
Most of these will be Windows 10 Home, which is good enough unless you want to connect to large work networks.
Ones to avoid are things like HP Pavillion, Dell Inspiron and anything Acer or Asus. Better options are HP <number>, Dell Latitude etc. If you want the larger style, something like an HP 250 g7 i5, 8Gb RAM, 250Gb SSD, Win10 Home is under £400. I'm struggling to find something similar in the smaller size... ...I know because I'm on the lookout myself
I agree with the Mac remarks. Mrs TB was using mine after she let some pixie smoke out of her (funnily enough, HP 250 G1) laptop. I had to take it off her before she smashed it in frustration.