Today, my sister-in-law flew from MCO to ORD, and then she will fly from ORD to YOW - all on UA.

She was booked to leave ORD on UA 6140 - leaving at 9:02 PM. She wanted to leave on UA 5856 - this latter flight was supposed to leave at 6:10 PM. It did have empty seats in the economy (coach) cabin.

She arrived at the YOW-bound flight's gate at 6 PM. Passengers were still boarding. When she arrived, the display showed that the departure time was supposed to still be at 6:10 PM. It finally left at 6:35 PM - the UA web site says that the delay was due to "aircraft servicing".

When she arrived, she told me that the gate agent (rudely) told her that there was no more time for processing of standby requests.

Although I would agree that such requests can not be processed 10 min before actual departure time; was he within his right to refuse to look into her request, as passengers were still boarding, and as ultimately, the flight departure was delayed by 25 minutes.