It will probably be more expensive at the airport.
I would maybe try your bank before hand or use an international credit card to withdraw at the airport like my parents did. But it depends on what kind of service your bank offers with that card. My mum had an international gold card with her bank and it was better to withdraw than go with euros to an exchange booth.
I live in Japan and I still do withdraw with my French card from time to time at the post office ATMs but recently I have been using 7/11 cash machine and always use the "withdraw in yens" instead of the amount of euros they show me because in the end it's more expensive than what my bank takes me.
Before you confirm the withdraw you can see the amount and if you think it's too much you can just cancel and try again for a lesser amount of yens.
I hate moving around in Japan in summer so I am no help when it comes to hiking lol.
In any drug stores they sell wet paper towels that stay cool quite some time and long enough you can wrap around your neck. I think she could buy a few and easily pack in her bag in case of reall hot emergencies. If she feels too hot, try cooling the arms pit, a former student of my husband who became a fireman taught us that
Here is the kind of products you can find in pretty much any drugstore.
46 cm long,
- 3 degrees celsius feeling difference
last about an hour