You're in Edinburgh, right? Let a couple of UK guys bang some parts out on that side of the pond.
Honestly, none of those sound like a decent deal. The last one doesn't even list what power supply it has, so it probably is using the crap one that came with the case. To install a GFX card you would have to replace the PSU too, so you might as well add 100 to that price.
For that money you should be able to build her a decent gaming computer. It won't be top-end, but she doesn't need one for what she wants. i wouldn't recommend the one pcboy has in his sig, but you can build a lot better for 300-400.