I’d tell her to replace it because there is clearly several nicks in the insulation/cover on that wire… perhaps the wiring underneath is damaged from being coiled up or cut or whatever..
other than that the yellowing could be aging from sunlight exposure ie that’s the part that sits on the desktop and sees most light (the rest dangles down to power point)
or it’s heat from electric supply that is degrading the colour of the white insulation.
Either way it is better to be safe than sorry