Her incompetence is really annoying. She always needs ten year olds to do her job for her. Also, it's inappropriate to wear makeup and high heels when you're an officer. Anyway, I'm not done yet and I've got a whole list of reasons I hate Officer Jenny (Yes, I'm treating them all as one character).
She's constantly giving Ash and friends crime-related information they have no need to know (and probably shouldn't know).
She's constantly getting assistance from ten year olds and sometimes she actively seeks it. In Black and White, in the Dragonite episode, she sought out the champion, prompting Ash and friends to aid her. When their aid didn't suffice, she rounded up a whole team of trainers to do her job for her. So here we see Officer Jenny is endangering civillians (some of them children) because she's incompetent and can't do her job.
In XY, a group of Malamar controlled her mind as part of an evil scheme.
She arrested a robot. You do realize those things can only do exactly what they were programmed to and are not in any way human? If you're going to arrest anyone, it should have been Clemont.
As I previously stated, her attire is ridiculous and inappropriate for police work. Fortunately, it has improved a little as the series has gone on.
Seriously, has she ever done anything right? Do the writers make her look incompetent on purpose?