Thanks terenz for the speedy reply.
If she signs up with a USA address, would she have a problem down the road when/if she wants to redeem an intra-UK award for 10,000 miles or a 20,000-mile Europe zone award (at least these are the mileage requirements for BA USA members). I don't think she has a USA-issued credit card.
If a UK resident registering through the USA is against the BA EC rules, please tell me, and I won't recommend it to her.
Are the award charts the same between the UK and USA programs?
Thanks again.