The MC is a commoner who gets a job at some sort of government post. But because the government is mainly nobles who looks down on her, literally everything gets dumped on her hands, and when she finally gets framed and fired for incompetence and goes back to her home village, it turns out she's pretty much the only one still capable of running the town defenses, because everyone else have lazed around.
^ your answer right there. Wouldn't recommend it though, it's pretty bland and doesn't do a good job of describing events. You'll feel like you're reading in a haze, only barely knowing what's going on.