She became Sheriff but it was destroying her so Dave stepped up to take the pressure off her
That’s if I recall some fiction correctly
I can't remember the specifics (or more helpfully, the "why?"), but this was part of the FAQ that AEG had when the relaunch was announced and not having Wendy as Sheriff was a deliberate story decision.
Thinking about the why of it all is that whoever was Sheriff was doomed from the beginning and they would much rather kill Dave than Wendy