i know its harsh but try shutting her in the room with the tray at night and smacking a rolled up newspaper on your hand or a squirt from a water spray and putting her on the tray in the day if she has an accident, she is probably a little stressed after leaving her mum so lots of extra love the rest of the time,i know its sad but i kept my tray in my downstairs loo and used to call my kittens to come with me whenever i went(they were following me around anyway) now all 4 of my cats dont have accidents anywhere unless they are ill of course if it carires on check with vet that she hasn't got a water infection good luck