Landline vs VOIP

AT&T told me that they need to replace my girlfriend's copper wire with fiber optics--she has had a landline with the same phone number for over 40 years that she is happy with and does not want to have her AT&T telephone service changed over ro a VOIP type of Internet telephone service.  She wants the secutity of keeping her landline, which is much more reliable during storms and hurricanes--and that she pays for.  My girlfriend is worried that if she lets AT&T change her copper wires to fiber optic cables that AT&T will also route her telephone number through an internet based service.  Will she still have her regular landline service as she has had after her cables are changed to fiber optic cable?  For the past three months my girlfriend has not had her landline working properly--her normal telephone number no longer rings at her house and when she calls me from her landline I see a completely different telephone number appear in my caller ID (on MY landline, or on my cell phone).  It's as if AT&T decided to change her phone number without her consent.  If I call her using that other phone number, I can call her on her landline at her house.  She called AT&T and asked to speak to a supervisor who told her that someone from AT&T will be going to her house on Sunday (10/29/23) between 10:00 AM and 12:00 noon to change her cables to fiber optic cable.  She only uses AT&T for her landline phone--she subscribes to Comcast (Xfinity) for her TV and Internet service and has no desire to change those for AT&T and she is perfectly happy with the Internet speed that she currently has with Comcast.  Can you reassure her that there will be no change to her landline service?