Free Speedup: Free speedup
Build: speed increase
Troop Size: increase
Helix Impact does a lot of damage to a single target, more importantly, it regenerates quickly. She does damage over time in the form of burning over 6 rounds, which can make or break a battle.
I think Troop skills that act as a kind of utility in this case increasing troop size, speeding up build time and giving players a free speedup kind cements the feeling that Scarlett should be leveled to 131.