Cheatle is quoted elsewhere as saying the roof in question was sloped and presented a fall risk for Secret Service agents - and that is why it was not secured by agents.
She should be dismissed for repeating what her handlers told her to say. She is not qualified to hold her position with the SS.
If there is a charitable explanation: the roof was not secured by SS agents because the baking sun made it uncomfortably hot so the team said not to fiddle with it because it was unlikely anyone at a Trump rally would act out.
The pitch of the roof the government sharp shooters was on looks steeper than the roof the murderer was on.