Have you ever wondered whether you could shoot someone.. if the situation warranted it? Now imagine pointing the gun at your self. Imagine the gun at your own throat or under your own chin. I think she held off until the point where it was either death or arrest.
But most people can't "imagine" your scenarios because their minds do not become altered to the degree required to carry out such acts. In SC's case she was diagnosed with a serious mental illness which her psychiatrist said would only worsen. Weeks earlier she had spent time in a psychiatric hospital.
What evidence exists that SC was alive after the police arrived?