She doesn't work really hard to do it, she orders people around lol.
Also, since this is the result of the case, it's not a mystery to begin with, just a misunderstanding and difference of opinion.
To be honest,
Oreki didn't lose this, like he said, they were given wrong interpretation of the information, their course was dead set before they knew it. Oreki's solution was only based off on the information granted, key information was not given, the solution could be only one.
She manipulated the investigation and made Oreki the neutral bad guy, after the conversation at the end she had with his sister, the way his sister ended the conversation by simply logging out, I'd say she had her ass handed to her. She should apologize but she won't. Like she said, she was in charge of not letting the project fail, and in her opinion the movie would be a fail, she was also in charge of the information.
No one told her to hide facts or hamper the original idea the script writer had. She herself has become what we all hate most, the greedy industry that only wants results and money and doesn't care about substance. It's true that Oreki's solution was great, but it wasn't true to the idea of the story that was supposed to happen. The writer did a mistake by not making sure about the poll, but even then once the script is prepared only the person in charge can make changes, and since the result must always benefit the person in charge, the ending result could not be as the original script intended.
Like Oreki said, it was never about solving a mystery, so this isn't a mystery. It was about writing a script that favoured the persons in charge opinion.
Oreki got annoyed not because he actually failed to solve it, since it wasn't about solving it to begin with. He got annoyed because she outright played them like fools. The same reason is why his sister logged out without saying anything. Instead of accepting her failure, she made an excuse.
There you have it, it's simple.
I did wonder why she did not appeal to me, she was pretty and cold and strict, but something was different, I didn't like her. Now I know why, she's like Bethesda and EA, results results results! money money money! That's her career path.