I finally had success putting a new HDD in a WD My Cloud single bay "NAS" (in inverted commas because it's barely a NAS) Man talk about a convoluted way of operation. This has been a project that's been ongoing, off and on, for a couple of weeks now, with every previous effort hitting a brick wall somewhere in the process. Even with a still usable (but slowly dying) HDD of the same brand and model as the replacement, it was still a PITA. You would think it was simply a case of cloning the drive... nah, not that easy LOL. Building the drive partitions (seven of them) manually still took three attempts before the NAS would recognise it and allow you to access the web interface, so that you could allow the device to rebuild and reformat the partitions to it's own liking.
As opposed to my Synology NAS, that I fitted two brand new drives to, without losing any data, simply by replacing the drives one at a time and letting the system rebuild the drives individually as they were replaced.
Anyway, it's up and running now, so the daughter will be able to stream her own music to a new digital streamer I got for her.
Anyone contemplating buying one of these devices, I would strongly recommend them checking out the alternatives.