This is actually something we talked about when she was first being designed! The main issue with it for us was that it meant that you were basically always staring at the ground as you moved around. We then thought about it as an ability where snowball would fly out in front of you and lay a path that you could slide on, but ultimately decided to try to avoiding giving her extra mobility.

From a game design standpoint, shes a hero that is more about slowing enemies and stopping them, rather than herself being fast. In general, we often find ourselves trying to resist putting tons of mobility on every hero, to make sure we keep every hero feeling unique.