In 2016, I adopted a female and a male from the same litter. All has been well with them until this summer. The female starting hiding in strange places such as on top of the fridge or in the closet. Then she started peeing and pooping in these spots. I immediately took her to the vet and they couldn’t find anything. She is her normal happy self just not using the litter box. Then I saw that when brother was around her she would hiss and coward down. He has never shown any aggression towards her except for playing. He never hisses back and really just seems to ignore her. She is terrified of him every time he comes around. She will sometimes go to the litter box if you take her and sit her in it. Then she runs quickly back to her spot in the counter. When it’s eating time, she has no problem with him and she’ll even start licking him. We’ve tried CBD, hemp oil, anxiety treats, and a pheromone diffuser/spray. Please let me know if you have any other suggestions! She won’t get off of the counter unless it’s for food!