I've been sent UK Starbucks cards in the US and sent US Starbucks cards to the UK. They work fine.
The money is kept in the currency it was originally bought in (so pounds if bought in the UK) and if she tops it up in USD, it will be converted into pounds, then back to dollars each she buys something.
As far as I see, there are no fees.... so, as aimlesstraveler said, it's a good way to get rid of odd money.
I've put GBP, USD and Canadian dollars on my card- no problem!
I'd suggest registering the card before mailing it if it's a large amount so you can get the money back if the card is lost- there's a little bit to rub off to get the pin code.
You can send those numbers to her first and she can register it herself (making an account on Starbucks.co or Starbucks.co.uk- they'll both work for registering and later accessing her account) or you can do it.
If you do it, you could top up her card periodically if you wanted- just tell her so she doesn't throw it away!
Starbucks has little mini cards now that can be put on keyrings.
I haven't seen them in the US yet.
There is also a special London one.
Besides the T&C on the back being different, I haven't seen any other different cards in the UK....
I worked at Starbucks for three years and I have been one of those excited baristas before seeing the foreign cards.
They are pretty cool.
