I'm afraid I can only commiserate since my Taranis is very like your Leila, a cat that would like nothing better than to have a home and guardian to herself and one who has had spraying/pee'ing issues for so many years that I know another home is out of the question. Taranis had already had 6 homes (if you count two stays at the Humane Society) by the time she was 3 years old. She was okay when downstairs only with Macduff, though she still marked, but I was forced to put a couple of other cats downstairs with her and things got much worse. She frustrates me more than any other cat because I know exactly what she wants and also that she won't get it - being upstairs (main floor) with me, left alone in comfort except when she wants to get under my knees under a blanket for hours on end, and with no other cats in sight or sound.

I do put her in a small bedroom by herself so she will eat, as far as is possible in a multi-cat household, only her diet food and she really loves it in there, would stay in there happily all the time. But she's also obsese (the only one) and needs to move so I have that door open most of the time. However, that room is not my bedroom, so it works out as it does not for you. I don't know your set-up, do you not have another bedroom that only she can inhabit?

About all you can do, I'd guess, until the money to extend your cat-run grow on the trees in your garden, is come on here and vent - sorry!