[madmmac]

Send back the unlocked phone and unlock her own phone. Buy the Sim card at the airport.

Do not take a debit card. Use a credit card only for the extra protection.

RFID slips, purse/wallet for chipped cards and magnetic stripped cards.

If not fluent in the language, an app for voice translations and an app translator for reading signs, menu's...etc.

Not sure if they are driving or Spains requirements, but they may need a International Drivers Permit. You can get them at AAA places in about 10 minutes.

Health and dental cards.

As noted, copy of Passport to leave or place somewhere else so if 1 gets lost/stolen you have proof to make it much easier to get replaces.

Be always aware and have fun!