If the event was open to all, and she was doing what was reported, which was being silent in prayer, and not blocking, disrupting, or destroying anything, and, apparently, not there when the facility was closed, by what authority was she to be removed? Would they have removed someone who was just sitting there, doing nothing at all?
“by what authority was she to be removed”
By the same authority that anyone invokes when they ask people to leave their property. You can question the decision all you want, go sue em for all I care, but if they ask you to leave that isn’t the time to question their decision, unless you just want to escalate the situation.