If I'm not mistaken all girls in TW3 share the same body in game , but the community considers Triss Ass and Boobs bigger than Yen, while Yen is more skinny and athletic
Nah there is some slight difference (as someone that extracted models from the game)
TW3 is a 10 yr old game so models are very low poly by today's standards, so it used tricks with normal maps to convey how skinny a character is for example. For example Ciri's ribs are visible with many visible "ridges" in her normal map, and side by side with textures she appears the skinniest of the three, while Triss looks the most "plump" (her normal map has less ridges than others). For most other females other than the main trio, the textures are reused.