Girls under Pressure is the second book in the Girls Series by Jacqueline Wilson. It was published in 1998.
After being called fat by a girl while waiting for her friends Madga and Nadine at a modelling agency event at the Flowerfields Shopping Centre, Ellie becomes very upset. She had always known she was plumpish, bigger than her friends, but that other people saw her as fat? This leads to her becoming obsessed over food and her weight, but will she see what she's doing to herself before she becomes ill?