Currency Changer not working for client

Sorry in advance. My client can’t use the currency changer on the website. She says it is visible but when she clicks on the alternate currency the page won’t switch between the 2 currencies and gets stuck on USD. Sorry I can’t replicate this fault, we are both using Chrome on Windows. I’ve cleared the hosting cache and got her to empty her cookies and cache. She is still seeing everything in USD with no ability to change. Have you any idea what might be causing her problem please?
Helen