Probably because someone is spoofing her number. Pay attention to the following, especially the last link
Caller ID Spoofing:
https://en.wikipedia.org/wiki/Caller_ID_spoofing
https://consumercomplaints.fcc.gov/hc/en-us/a ... ID-and-Spoofing
https://www.fcc.gov/guides/caller-id-and-spoofing
http://800notes.com/forum/ta-9f0ce767d8019be/a-different-spoofing-victim