1. Negotiation take alot of time. During that time people need to eat, go to the toilet and sleep. There also have to be breaks for the parties to ponder new offers and ideas.
The divine probably decided to go to a more private spot to think. The area is filled with templars and people loyal to the Divine. Dorothea is also an ex bard and capable of defending herself, she should have been able to survive by herself for 10 minutes.
So she goes to the hall (probably followed by someone to the door, they scan the room and then let her be). BAM an old god appears, backed by grey warden mages. Dorothea goes "Wft, why are YOU guy's helping HIM?!". BAM they cast the spell that binds her. Cory goes: "Keep her still guyz, we have like ten minutes to go". Quizzy, one of the few people doing their business nearby, hears the screaming and goes to investigate.
2. Quizzy open the door shouting. Concentration of the mages/Cory is disrupted (The bane of many summoner) and Dorothea makes the will save along with a split second decicion to hit the ball, which seems to be the focus of the ritual/closest thing to hand).
3. The ball is already primed to make a more sophisticated mark between the divines bosom. It smacks the ground in primed state and Quizzy picks it up. It's still primed, but a bit more wonky, thus makes a smaller, more wonky mark on Quizzys hand.
4. "IT WAS ONLY 10 MINUTES SER". She probably asked her guard for a few minutes in private, so the guard went for a ******, stood a bit away from the door, was momentarily distracted. Maybe he saw a few grey wardens who had offered to help defend the divine if the worst came to pass and trusted them (because of their new status of heroes after a recent blight) to keep an eye on the Divine and leap to her defence if something went awry. Maybe the grey wardens killed the guard at the doors? (Cory turned them into specks of Ash). Maybe her guards were sneaky infiltrators?
5. The ritual was probably just a 10 minute affair. The area wasn't heavily populated and the Divine probably wished for a few moments of privacy to pray/ponder the situation. Silencing her would have take even longer, and since Corpy is cocky and believes that he is the new god, he figured he could probably dispatch some lowly mortal mages/templars without any problems.