Is 5'3, 125 pounds fat?

It's not me. It's my sister. She had a physical & the doctor said that she's fat & that she needed to lose 10-15 pounds. My mom agrees with the doctor & tells my sister that she needed to lose weight whenever she's eating something sugary or just being a coach potato. I think she's just fine. She doesn't need to lose weight. Sure, she might have a bit of a belly, but she's healthy. Ever since the doctor called my sister "fat & needed to lose weight", she's been sobbing about it. Do you think she's at a good weight or is it bad? I really dislike my doctor too but for other reasons.