They never leave a message, and they don't call consistently. I get 3-4 calls a week, almost always at noon. Never answered, and they've never left a voicemail, so it can't be that important. If we all block them, they'll stop eventually, right?
Read up on your rights here, get template letters to send and also make a complaint at this government site: http://www.consumerfinance.gov/
Also file a complaint with your State Attorney General's office.
List of State AG’s offices: http://consumerfraudreporting.org/stateattorneygenerallist.php
Block the calls. For a smart phone a call blocker is an app. Her phone may have come with one or she can download a free one. For a simple cell phone ask her carrier. Or put the pest in her contacts list with the ring tone "no ring".