a mac
PC = waste of time
For £600? You'll be lucky.
Depends what her priorities for & what she's using it for. Whistle stop guide:
Acer - Generally known for being best value, spec-wise
Samsung - Look nice, good compromise between spec & looking shiny
Sony - Good build quality but can be overpriced
Not sure I would go for any outside these brands, I've had a Sony, a Samsung laptop, Samsung netbook & Acer. Sony died after about 4 yrs but this was a few years ago now. Samsung's been going strong for 3 yrs and battery hasn't even died yet. Netbook is a few months old. Acer is looking good after about 6 months & has by far the best spec of all of them, unsurprisingly.
I'd read some user reviews on amazon or dooyoo.co.uk. I don't tend to read 'official' reviews posted by tech sites and the like because they tend to fall into one (or more) of three categories a) used the laptop for 5 mins b) compare it to previous model in range, which is misleading and c) sponsored & so encouraged say good/bad things by manufacturer or competitor.
I'd start on Amazon and search by price, then use reviews & spec to narrow it down. & probably a good idea to come up with a few options - you know what us women are like

Plus, if she ultimately chooses it, then you can't be blamed for it!