Vintage Paw
dead stare and computer glare
She could still be picking up "other cat smells" and is marking her territory - Rusty (Hellspawn beast, from Hell) took to weeing at the top AND bottom of the stairs EVERY. FUCKING. NIGHT. for far too long - but it ran into months and possibly years - she had unlimited access to outside - and this was the problem - outside had unlimited access to inside, and there was an interloper and Rusty was protecting her territory - Bob just couldn't be arsed, so protection duties of the "hoomans" fell to her
I think this is the most likely thing. My doormat is brand new, so shouldn't smell of Charlie. And Charlie didn't especially spend any time by the back door where she most recently weed, so I wouldn't have thought she was drawn particularly to that area, but it's possible the general smells of him could trigger stress on occasion, and the back door that leads to the place where interlopers could potentially come in would be a good place to mark, in kitty logic. It's entirely possible there's been a cat coming in the back yard, and she has uber super smell ability and can tell it's been there. The way she's been sniffing at the door cracks suggests something along those lines.
She went in her tray yesterday and this morning as normal. She seems chilled out.
I've been furiously going round in various corners with the feliway.