And the big smug face of her when she says it
Her smug face is just a way of her to cover how she is feeling insecure. She will always want what others have and measures her worth by how she is doing compared to her sisters. Donna has the business, so Sarah has the 'business,' , Donna had the wedding so Sarah must have the fancy wedding, Donna and Kate had the babies so Sarah must have the baby.
Sarah is too insecure in herself to think about whether she wants these things, I wanted a light up jumping rope when I was little because my sister had one, but I grew out of it, Sarah never did.
This is why things do not work out for her, she only wants what others have, not what she may want herself, and she is jumping in headfirst with Keith to get the baby girl that Kate has.
Until Sarah acknowledges her alcohol and food problem she will be forever trapped in this cycle of trying to be like her sisters, medicating with alcohol and starchy foods to comfort her and make her choices feel ok.
Her mother should feel ashamed of herself by promoting such a culture between her daughters but I feel that is the way the mother grew up too, same alcohol dependence and all.