When my Cassie died many years ago, Beau pined for two weeks, he took almost no food. By the end of the two weeks he was emaciated and I was sure I would lose him too - the worst thing I could imagine.
When he finally started eating again it was chicken roll rather than cat food he would take (i had tried everything), albeit fed by hand in an intimate and private setting (we sat together in the porch with no-one around, him on my knee taking small pieces in silence - no purrs, no words - just strokes and cuddles).
Since then whatever has befallen Beau has been remedied with private cuddles and chicken roll. This is his comfy place. 12 years have now passed and he never really got over Cassie - he was so carefree with her in his life and this joy never really returned - but this combination works for him, and it must be said, gives me some comfort too.
There will be a combination that works for you and Cleo. Please persevere trying different things in different places, find her comfy place, she will come back to you so long as she feels your love.