You obviously missed the news where it said of those who took " selfies " were narcissistic.
Sheila was forever conscious about her appearance. She worried after the twins were born that her figure was " out of shape " and that she'd become too fat to continue her modelling.
She could have just been insecure about herself.
It wasn´t her that wanted to be a model in the first place, Colin suggested it to her, which was a shame, BTW, because she was not fit for that cut-throat business.