You should be able to pop
Gotta Save your wyvern poison for her, i believe Astarion can prock it 3 times
BattleMaster Lae'zel can terrify her as well
I always use the wyvern poison on Priestess Gut so she doesnt call for help.
you should be able to burst Gut before she can call for help without wyveen, agree to go to her private chambers and have Astarion stealth and sneak attack her