I don't have a direct answer to your question, but..... I found exchanging dollars for Czech Koruna to be very easy in Prague 2 months ago, and the conversion charges were very reasonable. There are exchanges everywhere and they must have a sign posted that details the exchange rate. After walking by a few you will quickly figure out who has a decent rate. Now will a 15 year old be able to do this? I don't see why not but I don't know her of course.