As the FA I would have called the Flight Deck to resolve the problem. That's what i am supposed to do. Final checks in progress or not.
I would have said to her as the Captain;
"OK, make your call".
And if she insisted on being disembarked after it I would have gone back to the gate to offload her asap.
Exactly as I would do if a passenger suddenly became very ill, or disturbed, at any moment prior to take-off.
Massive disruption, etc etc. **** happens from time to time.
I am aware that in these days of fear of consequences a Captain may feel he/she needs to discuss it with Head Office before doing anything out of the ordinary, but your question was "what would you do?".