Is she going to shoot Mycroft? Or is it a race against time before Mycroft collapses with lack of his medication.
Thinking out loud here take or leave it, -if she's pointing a gun at Mycroft --
Maybe Katrina trusts Sherlock to be honest and tell the truth that Mycroft didn't arrange the killing or if he did arrange the accident for national security he gave them a new life under new names etc. Sherlock deduces that maybe. Maybe he mended her enough that she'd listen.
Last post for today. Sorry.