Yesterday a miracle happened ! Pookie came back to my room. She sniffed around and finally sat down on her usual place besides my computer.
The first still timid approach
But then she climbed on my (unmade) bed and settled down to take her nap. Little Rosie jumped on the bed too and after a while collapsed there too. When Pookie was gone for a few moments I quickly made my bed and as soon as it was done, they both came back
and slept together the whole afternoon (with some interruptions for Rosie to play)
and in the evening, they both came on my knees ! Pookie still is not totally assured that Rosie is not a competitor to her but it's already a good beginning. Rosie quickly learned not to go too near to her, because then she still hisses.