Except that you're not standing in the queue to be processed by the bouncer, but you have a valid ticket, which they sold to you.

Venues should be required to refund tickets if a person is denied entry provided they weren't previously told they were banned from the venue.

If you buy a ticket, you can't just unilaterally decide that you don't feel like going after all and get a refund. Why should the seller get to do the equivalent?

The law firm were notified prior (2x) that employees would not be allowed entry to MSG. Having been so warned, she bought a ticket and tried to go.

After having been warned and then being prevented from going in, her response is to sue them again.

I don't think notifying her firm is good enough. She should have to be notified individually, directly, and provably for them to get out of refunding the ticket.

It wasn't entry to MSG, but entry to radio city music hall which is owned by MSG. It's not clear how obvious the warning was.

If they have the tech to identify everyone individually they don't want going to their venue, then it's on them to notify everyone individually ahead of time. Otherwise, refund + expenses.