Teaching an older cat litter tray habits?

I took a 12 year old in on Thurs, just until the woman who runs the shelter is back on Mon. She hasn't used a tray for years, and while she knows where it is and what it is for, her attempts at weeing in it go wrong, as she ends up standing up and wees on the wall!! I have just witnessed this!! I have limited space in the bathroom to move the tray, and can't move it too far from a wall. I have moved it so it is closer to the toilet (might be easier to clean down than bare plaster). Anybody any other suggestions?

Is there enough room for a covered box?

MKD

Not sure and she is supposed to be going tomorrow or Tues. She didnt miss overnight, so maybe it was just too close to the wall (although the other 3 cats that have been in there haven't had a prob!!)

We've put up a backing piece on the wall to save it from similar things, so you might consider trying it... even just a couple of short pieces of panelling, or even the litter tray cover might help.