Bit of a property A&E here…
So one of the two wheels on bottom of sliding shower door has broken off. Doesn’t appear I can simply order a new wheel.
I can try superglue first but can’t see that holding too long.
Any other suggestions? Effectively, the wheel’s job is to hook into bottom of shower frame. I could try creating something else to hook on but that might mean hammering into the shower door frame
Superglue… not a natural DIY’er me thinks 
How about get a temp shower curtain for the moment if you think that would work, Ikea be less than €10 I’d assume if you are close to Ikea, even argos or some other store. You should be able to cable tie it to the top rail. Simples. Removed the one or two existing sliding doors. Hey presto. OW’s consultancy invoice in the post. This temp solution, may work for you for ever and ever. Seriously. 
My experience as a user of thesis shower door systems, the older ones, are just a breathing ground for dirt you can never clean, like real funky gunky colonies, living colonies who knows how many species of trillions upon trillions of bacteria - the newer systems are more minimal, often hinged door (glass too, easier to clean that plastic that scuffs), the sliding thing doesn’t really work except in cramped space but creates surfaces impossible to reach and clean… oh yea, Irish housing. Tiny.