That’s exactly why she used that excuse, to look absurd. If you are responsible for the former President being nearly assassinated, better to have it believed that it was due to stupidity than to something more nefarious. Same thing with showing up to the hearing completely unprepared.
I don’t care if she wasn’t the most qualified person to head the SS. Doesn’t matter. No one with 30 years experience in security could be as inept as she is coming across unless it is an intentional act to appear that way.