Great speech, she had lost weight.
Assuming from your name, you are a girl. Sarah seems to have the “skinny gene” (wish I did).
She could probably drop 3-5 pounds within 2 days....where as I, would take a while.
She is also small boned. Even just a few pound weight loss will show on a petite boned woman.
Besides, as a woman, the clothes you wear can take off or add on poundage.
Nothing to worry about.