Observation: Catra’s physical strength appears to vary wildly from episode to episode, and sometimes even from scene to scene within an episode; sometimes she can casually put her hand through a three-inch steel plate or physically overpower a monster hundreds of times her size, and other times she seems to be scarcely stronger than you’d expect any reasonably athletic twentysomething woman to be.
The Likely Explanation: Catra is as strong as the plot requires her to be, so the writers didn’t keep particularly close track of whether her demonstrated physical might was consistent from scene to scene.
The Angsty Fanfic Explanation: Catra has some sort of unresolved mental block about using her full strength, probably stemming from some Terrible Childhood Trauma™.
The Fun Fanfic Explanation: Catra doesn’t actually know how ridiculously strong she is, because she has no standard for comparison and it’s never occurred to her to put it to an empirical test. When somebody (probably Bow) notices the inconsistency, this inevitably leads to her being challenged to perform a series of increasingly inadvisable feats, culminating in some comical disaster that frames a Very Important Lesson™ about why needing to prove oneself to others is an unhealthy impulse.