Mhmm.
It's not instant my any means,otherwise she wouldn't feel the massive amount of pain.
Whilst if we strictly speak about the brain,they've got three minutes before the lack of oxygen begins triggering permanent damage,four to six minutes in which her being saved would leave her in one of many mentally damaged states or straight up a vegetable,and after that the reaper comes' reapin'.
10 to 15 minutes after is when professionals would declare death.
The instant nerve ending seperations could cause immediate unconsciousness,though,and "could" because the few studies done on beheaded folks found out that some would still be conscious until the blood completely drained from their heads,which would take quite a few seconds,if not a minute,due to how close the cut was.
So it's not movie level,but a very slim margin.