Hm, I'm now 90% certain she did it. Friday and Saturday passed without incident, but yesterday I was in the kitchen with her and she went to her bowl and legs both sides and squatted as going to wee. She has got one like this, so I presume it's quite easy to balance as it doesn't really move due to rubber bits on the bottom
https://www.amazon.co.uk/Hing-Designs-C ... +food+bowl.
Before she could pee, I picked her up and took her to the litter box and she did her business there (now I kind of wish I just let her do it, so I could be 100% sure).
Afterwards when I removed the bowls for a bit she was just walking over the fish. Such a strange thing to do.
Her water and food are clean, both bowls get washed daily and she is eating her food. Her litter tray is also clean and she uses it all the time. She has always had the same bowls so it can't be "i don't like this new bowl, so I'm going to use it as a toilet instead" kind of thing, so really don't know what's bothering her.