Loads of choices. Most netbooks are pretty standard fair with a few tweaks here and there (bluetooth, matte screens, bigger batteries). At this price point ,They all revolve around the same Atom Processors N270 / N280, 160GB drive, 1GB ram, and 1024 x 600p screens.
Some more expensive models have got Ion graphics for HD videos and even some gaming, with a 11''-12'' 720p screens (much better for internet browsing as well).
Some of them have 'attractive' colours, they have a pink Sony Vaio (£250) here at OcUK, the Asus EeePC comes in various colours, as well as Dells, instead fo the old boring black.
I'd pop down to your local big retailer and sample a few, see which one she'd prefer. Quality and feel varies. You don't have to buy there, but if you want to stick a second 1GB RAM stick, there are usually a small trap door at the bottom, same for the hard drive. Many models come in various configurations, but share the same basic platform.
Personally, I'd recommend a High Res Screen (1366x768) as 1024x600 gets quickly annoying, since web pages are usually optimised from laptop screen resolutions, upwards. Given the budget, it could be difficult though.
You'll be stuck with Atoms though. I'd consider a Ion if watching HD videos are on her agenda. Atoms can barely decode 720p, so you need a graphics card to help you out. Ion netbooks usually have in general poorer battery life, but still pretty decent (5-6 hours).
You may struggle to find a Ion netbook (HP 311c) for under £250. Anything around £300, and I'd seriously consider a 13'' notebook CULV instead (can be had under £350).
If you just want a standard netbook, then I'd say a trip to local retailers for a quick look would be your best bet, then we can advise on the models you preferred.
I'll give it my best though. HD videos aren't on the agenda, just YouTube videos. 