Don't forget there's still some question about her claims of having owned a stun gun(as opposed to a taser) both in testimony and in her journal.
Something just strong enough to stun him and possibly make him obey her command to sit in the shower, it would definitely make one wary of getting zapped again but not enough to totally disable a person. That would be all the time she would need to pull out her knife and start attacking him. As for the gun, I still think although that may have been her initial plan, it likely jammed on the first attempt and after butchering him she unjammed it while standing over him and then shot him(take your pick for reasons, to confuse the police with the possibility of two attackers as it seemed she had planned, to make sure he couldn't possibly survive, or just as a final fu).
Anyway, thankfully JSS came through with LWOP and hopefully none of her appeals will make it past first reading.