Unmodified HTC One Mini stuck on Bootloader

[AC Question]

Hi, my daughters factiry unmodified HTC One Min has somehow got on to a white screen headed "LOCKED" and with a number of options including "Bootloader" accessed with the volume keys

Nothing I try gets it off this screen - even " FACTORSy RESET" just returns to the same screen.

Any assistance for getting the phone back to normal greatly appreciated.