Q: Lost photos on iPhone after factory reset

If the photos only existed on the phone (i.e., if she never imported them to a computer, never turned on automatic iCloud backups, never backed the phone up to iTunes, never turned on iCloud Photo Library, never used Photo Stream to stream them to another device, never used a 3rd party app to send them to another device, never used Dropbox to store them, never used Flickr to store them, or a number of other options that I can't think of right now), then unfortunately they are gone. Hopefully something in that list might jog her memory as a possibility that she can check to see if she might have done and forgotten.

As she is probably now well aware, a phone is a terrible place to keep the only copy of anything important. In addition to possible technical issues, it is constantly exposed to risk of loss, theft, physical damage etc.

Another thought: the one thing that she may most likely have forgotten that she may have done is to turn on iCloud automatic backups. The following link has information about how she can see the date and size (and also delete -- but obviously don't do that) of any iCloud backups from another iOS device if she has one or from a Mac or Windows computer. See the Backups section of Manage your iCloud storage - Apple Support