That's the thing. She is not a normal human. She doesn't have visible muscles in this game because she never trained before. But because of her giant essence(one of the character classes for a future game) she can do such feats.
I hope this image will help you with her body shape. It doesn't have to be exactly the same thougth.
I saw an AI art of Tifa in a YouTube video earlier but since they changed it I am not able to provide one but that's face I always imagine when I think of 3D Hailey. This image below kind of look like her just her eyebrows are little thick.
