|You are of a fearful nature and you instinctively know how to make yourself scarce in order to avoid any and all attempts at physical contact.
A character who can Sneak is able to walk past people guarding a room, and is harder to hit in melee (both knife & hands attacks).
As guards are usually employed to stop Mush, the main benefit of this skill for Chun would be the added safety. In combination with the Plastenite Armor she should be wearing, this can make the "classic rampage opening" of killing her rather costly.
In the rare case of a Pacifist or Mush Mutant using guard against your team, the other part can also be handy of course.
Stephen may be tempted to copy this as Mush, to improve his own mobility and defensive prowess.