I had the idea of the lonely literally draining colour out of it's victims

Which she does!

…but then she gets merc’d by another fear power and wakes up back in S1 of the Magnus Archives again.

Basically Sasha pulling a Groundhog Day and gradually getting further and further with each run before getting bumped off by a different power every time.

And she eventually does it! It took over fourteen goes, but she’s got Jon and Tim and Martin all safe and sound up in the safehouse in Scotland with her. She did it. She won!