I was asking because last time I went to her chamber I closed the door behind me and when I killed her everyone in the area breaks the door in and I nearly lose my party
If she gets an action she will cry out, raising alarm.
If you can't kill her before she gets an action then try to use silence on her or, as mentioned above, hold person.
If you allow someone--not an elf or half-elf--to drink the potion and fall asleep then you don't even have to kill her. When you're locked up in her cell an NPC will come to help you. That will be the end of Gut.
