Force [fawrs, fohrs] Show IPA noun, verb, forced, forc·ing.
noun
1.
physical power or strength possessed by a living being: He used all his force in opening the window.
2.
strength or power exerted upon an object; physical coercion; violence: to use force to open the window; to use force on a person.
3.
strength; energy; power; intensity: a personality of great force.
4.
power to influence, affect, or control; efficacious power: the force of circumstances; a force for law and order.
5.
Law. unlawful violence threatened or committed against persons or property.
Therefore, Force = How much damage your weapon will deal when it hits.
For example, A weapon with 12 Force will deal 12 Raw Damage (at 10 STR/TEC depending on whether it is a Main Weapon/Homing Sub Weapon or Melee Weapon) for every bullet that lands or every swing that lands, but consecutive hits will deal less damage due to Tough Reduction. Meanwhile, a higher Force weapon will deal more damage per shot. For example, at 10 STR, a 25 Force Melee Weapon will deal 25 Raw Damage a shot, and each consecutive hit will deal less due to Tough Reduction.
Litia stuns pretty hard, and her force is rather low. I don't have her, so I can't say for sure, but based on stats I would maybe tune x2 Slow and x1 Grappler or maybe x2 Slow and x1 Gladiator