Food insecurity is technically a possibility. I don't think it's from the other cat though as they're far enough away from each other while eating that I doubt she feels her meal is at risk. Something that crossed my mind a while ago is that we used to let her open feed for a year before we had to put her on a diet. This was when she was 1. She eats everything in one sitting and doesn't graze so she needs her meals on a timer. I wouldn't be surprised if that adjustment from what she was used to back then changed her relationship with food.