Hi Stella
Sorry - I said Tilly in my other message, I obviously don't read carefully
!!
For the first few months after bringing Meisha home she sometimes used her litter tray & other times would wee & poo on the sofa. I tried discouraging her away from the sofa (you can do lots of things - I put tin foil over the sofa cushions while we weren't at home, you can spray weak lemon juice [cats don't like the smell], I think there are even some specific sprays in pet shops that are for discouraging cats away). I was advised to try to see whether anything caused Meisha to do this - but as we work full-time I never caught her in the act so don't know! In the end I changed the amount of litter in her tray, kept it fastidiously clean and tried a different type of litter & finally I managed to find the perfect combination as she uses it consistently now.
As Suki is only weeing upstairs I wonder if it's not as simple as just 'litter tray rejection' .... it may be she has a urinary infection & so I would go & see your vet to rule that out. Or she may be feeling anxious for some reason - have you ever tried Feliway? I've got the diffuser which has calmed Meisha down which may have helped with her litter tray issues. Is there anyway you could stop her coming into your bedroom for the time being until she gets into the habit of using her tray each time?
Hope something in my rambling has been helpful! Sas