Cait's perk is called Trigger Rush. The perk is originally meant to increase AP regeneration by 25% when you are below 25% max HP. However, a bug causes the perk effect to change. Instead, Trigger Rush gives you 50% faster AP regeneration when you are below 25 Action Points. The bug can be fixed with the Unofficial Fallout 4 Patch Mod on PC, reverting it back to its original effect.