Sorry to hear that! I presume you have also looked at the two USA based callback "dinosaurs":
Enlinea International Telephone Calling Overseas Dial Direct Discount - international callback,direct dial,international long distance,toll-free forwarding, local newspapers, local weather, dictionary, translator calling card and VoIP services
Callback World - callback service for country to country calling
By the way, I know it sounds obvious but do you have any idea if she can call Spanish 900 (freephone) numbers? If so an account based service maybe a good option.
Also I think it was asked before but there are loads of gateways (even to UK mobiles) using special 901 and 902 numbers. As the rates to call these are supposed to be fixed (by Spanish law AFIK) they maybe cheaper than what she is paying for standard rates.