Hello,
If the Blackberry phone is locked with a certain US provider it would need to be unlocked before being used in Europe with a local SIM card. It wouldn’t hurt to ask the customer reps in Spain before buying a new phone. Sure, less fancy phones can be quite cheap in Europe so this will likely be your daughter’s best option. With a prepaid package over there she will get a regular cell number you will be able to call without any problems. Note that you will pay international charges that are higher than what you would pay for calling fixed lines (the good news is that only you, the caller will incur charges). Make sure you know the rates before calling (calling cards are usually the best option when dialing abroad). Your daughter will also be able to call you using her prepaid cell, but rates can be a bit high.
Here’s what you will dial for calls from the US to Spain and from Spain to the US.