You could try putting something of yours, that is well 'worn', into her plush bed, so that your smells transfer from it into the bed - this works every time we get a new dog bed. The cats, however, sleep where they jolly well like - currently the top stair, not even the landing!!!
Cats are so contrary. Love them to bits. My parents have a cat who used to get inside carrier bags given the opportunity and then attack peoples ankles as they passed. Painful but funny. He quit doing it when he got his head caught in one of the handles and just lays on top of them now giving them a "tickle" to make the rustling noise.
One of my own cats, give her a soft comfy bed and a cardboard box. She'll pick the cardboard box. Its more fun apparently. lol
Hester's favouite place to sleep, at the moment, is the second step down on the stairs. Woe betide anyone coming down quickly and without due care. She'll have a new favouite place in a week or two. She's an old lady (fifteen and a half) and does what she wants to do.
In my experience (having spent three years working in cat rescue so I got to know a lot of cats) it's simply because they can. My current cat (Dylan) has an obsession with sleeping on the windowsill in my bedroom when I keep putting him on the bed so he can be comfortable but apparently the windowsill is more comfortable.
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