The Giant looks good. Maybe a bit over priced at £700, but on the nail at £500.
Other brands to look at: Specialized, Trek and Kona all do women's specific bikes. Mrs Nerd has a Trek 4500 from a number of years ago. A bit heavy bit rides well (so I've been told, it's like a BMX for me!
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Look for: a Rockshox fork (they are the best in terms of reliability and ride at the budget end) of about 100mm travel, hydraulic disc brakes and Deore components.
Also look for a slackish head angle, under 70 deg as opposed to something racy (usually 70 to 72deg), unless she's going to race.