Vyper somewhat feels like Pyro from TF2: insane DPS but needs to be really close to make the most of it. But it's way too easy for her to get close, especially with the Slide and Stamina privileges she gets.
Other then nerfing her DPS and movement, I don't know how else they could balance her. Maybe heavily reduce the primary fire's range, and include a weak, single-shot secondary fire with longer range that could be used to secure souls in the early game?