We had this exact scenario play out at Hollywood Studios during last year's Moonlight Magic. My wife had a last minute work appointment pop up and had to fly down the evening of the party. We entered the park just about as early as we were allowed. She did not make it until about 9:30 pm. After a bit of back and forth with the cast members at the gate, she was let in, and given her snack vouchers.
I believe we were shown some grace due to confusion and rules being changed for MM entry recently. We asked 3 DVC CM's day of and were told by all 3 she would be able to get in so long as all our tickets were not used at the time the rest of the party entered.
I'm sure there is a good reason they've changed the entry process, a little hard to see from our point of view.