Is your bathroom big enough to put the other litter box in it, and show the kitten where it is? I'm just thinking - if that is where it decided to potty to begin with, you might want to go with the flow (so to speak) until a home for the kitten turns up (I know, I know...but some day).

Given that the kitten picked a particular spot, maybe s/he is feeling territorial with a lot of other cats around. This individual kitten just might be quirky that way!

I am glad the feral girl is back. Take heart - she didn't hide from you for days and days, so she may 'come back' more than she is now. Glad she reappeared...are you able to see if her neck is healing? Was the vet able to treat it at all?

HUGS - you're a great meowmom!