Yeah who the hell is still changing up money before going abroad loll
It's always good practice to have some local cash when going abroad. Even if you plan to mostly use your card.
In most countries, you can still find places that don't take cards. Or there could be an issue with your card not working...
Taking euros instead of francs to Switzerland is a funny mistake. But in the grand scheme of things, it's not a big deal... she could exchange her euros at any point and it wouldn't be a problem. Being stuck in a foreign country with no cash and no working cards, however...