Spoofing a private number (or is it called something else?)
It sounds as if some nefarious person could have cloned her number and be making the nuisance calls, leaving her number to show up on the recipients' call logs. Is that possible?
I've advised her to register her telephone numbers with the Telephone Preference Service and shown her how to report nuisance calls, if she also gets those - but this is a different problem, which I can't think how to help her solve. Any brilliant ideas, you clever techie people?