I don't think her resignation should have been forced by politicians - they have their own agenda. Incidents are investigated independently - yes she is in charge of the met - but is she responsible for every single thing that goes wrong - no. Should every one at the top resign when there is a failure lower down - no, although clearly it depends on their role in any incident.
I think she has been an easy target as she cannot fight back in the same way that Boris Johnson does when there is an issue, she has been very professional in the way she has responded to criticism she can't deflect in the same way politicians can. The rules that govern police forces mean her role is very regulated just as her predecessors, police forces have and will continue to face challenges and issues - they will be the same and their leader will for the most part deal wit them in the same way as the regulations allow. I think she should not have been forced out, however, for her own sanity she might be better off away from this situation where she has been the subject of often unfair criticism to which she is powerless to respond.