She could be an 8. Somewhere along the line they recalibrated women’s sizes. I fit into vintage items size 6, but modern size 6 hangs like a tent.
Probably closer to a sized 10 or 12 from pics I’ve seen. Either way, she’s not “fat” but perhaps could stand a sound fitness routine at the gym - 40 minutes of cardio and some strength training several times week could benefit anyone, no matter the size.