She was in charge of the operation that saw the Brazilian shot dead at Stockwell Station well before she got the top job. She was clearly earmarked for the job because she ticked all the right boxes that weren't important. Her judgement appears to have been suspect in many of the major problems in the past few years although, to be fair, she was finding herself in a more and more impossible position with a Mayor who was happy to allow BLM and other protests/vigils that were hijacked by the usual suspects and then conveniently blaming the police.
Whoever replaces her needs to be a big enough character to tell Khan he's running a police force not a branch of the social services and to butt out but we all know it will be another patsy...