My friend flew up to Seattle for a surprise party and got a round trip fare from PSP to SEA of around $340.00 on the internet. Today she was checking her Visa bill and found the charge was over $500.00 which was more of a surprise than the party. It turns out they quoted the price in British Pounds.
This really seems like false advertising as she would have never picked that flight for that price. Has anyone ever had an United States company charging in foreign currency?
Any suggestions?

If one logs on to Expedia.com (i.e. the main US site), then prices should be quoted in USD. However, one can also go to expedia.co.uk and get the same flights, but there the prices will be in GBP.

Assuming that for some reason she did use expedia.co.uk and they quoted the price in British pounds, the prices there are clearly marked with a pound sign. How would that be false advertising?

Expedia has 6 countries listed on their website. Somehow your friend got UK.

Did he pay the exchange fees?