As she should be.

Yep. If someone gets a clear line of sight on a protectee and is able to shoot at them a half dozen times, then your agency has failed catastrophically. That cannot happen without something having gone horribly wrong that should not have gone wrong.

She was always going to have to resign. Had she done a halfway decent job finding out and explaining what went wrong, she might have held her job a few weeks more. The investigation into this will require both the perspective of the people who screwed it up and independent folks who come in to figure out for themselves how the former people screwed it up. So if she had been useful in presenting the story of the people who screwed it up (including herself), she might have been allowed to finish up that task. She wasn't, so she was no longer of any use to anyone, and had to go.