She is incorrect about gate clearance (DM) as far as I know. Many agents don't know what they're talking about, as most of us at FT can attest.
Here's what I received from a customer service email not long ago. It matches what
lucky and others have observed.
As you know, our agents are to follow a
clearance order as follows: passengers denied boarding on earlier United
flights, passengers from cancelled United flights, United
misconnections, and then full fare revenue passengers. For all other
customers, priority is further divided by Mileage Plus status - 1K,
Premier Executive, and Premier, fare paid and check-in time.