Hey Gav,
Thats a very weird problem, to be perfectly honest, I have seen it before where people could not get setup using anything other than a WEP key, but I never found out why that was so, or how they fixed it.
But, if its suggesting there is too much noise on the line, it could be the frequency its on is being used by another device, thats my theory on that. Have you also tried moving the router closer to your gf's computer?
Hope someone can answer you better than me

Basem