"results after slit throat" and "reflexes after slit throat" mostly reference makeup effects and video games. Just "slit throat" had some useful information -- Carotid vs jugular, an actor who got a non-prop knife and did it accidentally but survived-- a lot of news stories about surviving, actually, which is disconcerting as both these characters need to die, ideally quickly. "slit throat windpipe" was the most fruitful by far, giving timeframes and blood expectations. Variations on "slit throat treatment" mostly pull comparatively minor cuts, or one paper on treating some failed suicide attempts, but those people had already been mostly stabilized and now just patched up. (Incidentally, google seems to automatically consider "slit" and "cut" as synonyms, using it in quotes to cut that out leads mostly to news reports again).
I have that the carotid is closer to the front than the jugular but is made of stronger stuff, and that hitting it would produce a bright red spray which diminishes quickly but continues to noticeably "spurt." Cutting below the larynx means no voice. Unconsciousness estimates are from one to three minutes with death shortly after.
My remaining questions are 1) Am I even on the right track when I assume they can do this well enough to reasonably-ensure their deaths? and if yes, then 2) What happens between when the deed is done and losing consciousness? Thrashing seems to be a given, but for example does she drop the knife, or are her fingers locked around it? Will they display pain or go pretty much instantly into shock? 3) What are my woefully underprepared paramedics going to try to do?