1. There won’t be any gain without some pain in this transaction. Make it easy for her. Take the hit and change the money into czk at your home bank. She won’t have time during her class trip to go running around trying to exchange currencies, especially since we’re talking about a relatively small amount of money. There wouldn’t be enough gain for her.
2. Will she have access to a debit card? If so, tell her to only use it at a post office or bank ATM, not some generic ATM machine on the street.
3. Hopefully, if needed, she’ll have a “no foreign exchange fee” credit card.

Hope she has a wonderful time on her trip.