Half a coach seat (revised)

My mom is a flight attendant for Delta Airlines so I have been fortunate enough to travel more than the average person. One of my favorite places to visit is Hawaii so my mom will fly lay overs to Hawaii every couple of months and let me tag along to take advantage of the free hotel room. This particular story is about my flight home on one of those trips when I was about fifteen.
I got to my aisle seat and sat quietly waiting for the rest of the passengers to board, I was really hoping that no one would be sitting in the rest of the row so that I could stretch out and sleep. Unfortunately this was not the case, a very large woman stood beside me looking at her boarding pass and the row number, and informed me that she was in the seat next to mine. I moved so that she could get into her seat and get situated, as I sat back down she wiggled uncomfortably because the arm rest was going into her side. I should mention that as a non revenue passenger at this time I was required to wear dress clothes every time I flew and I was supposed to basically sit down and shut up and it was an unspoken rule that I could not ask for any special treatment or complain about my seat.
This woman probably weighed in at around 300 pounds give or take some so she asked me if I minded if she lifted the arm rest up. I was absolutely terrified, I didn't know if I was allowed to say no but I really didn't want to have to share my already small coach seat with another person. Without even waiting for my response she started to lift the arm rest, but at the same time my mom, the flight attendant for this flight walked by and abruptly pushed the arm rest back down and said "This needs to stay down the entire flight. Thanks" and smiled politely at the woman. The lady looked disheartened but I was so relieved. This all happened in a matter of minutes but had my mom not walked by right then I may have enjoyed seven hours of half a coach seat.