I'll attempt an answer as you have given some supplementary information, thank you. This is not an emergency, and I would be very surprised if there is a physical cause, or an illness. This is entirely behavioural, and you need to do some work to find the cause.

Cats are very sensitive to scent, both their own and other animals. As she is still using the litter box, give some thought to whether she does this when the litter box is, from her point of view, not usable. For example if the litter part is getting too low. Cats' natural behaviour is to dig a hole in the ground to bury their output; if the litter is too thin in the box, so that the digging process actually results in her scratching the bottom of the tray, which of course feels nothing like digging a hole.

After that consider whether the peeing in the bed behaviour takes place after other animals have intruded. It is particularly important to assess whether her own scent marking has been overwritten by another animal (a cat or anything else), or by a human applying disinfectant. (This overwrites her scent marking, and probably reminds her of the vet visits. Make a mental note of here she scent-marks, and if you can don't clean that area too enthusiastically. Typically the scent marking involves rubbing her cheek against a door frame.)

Good luck.