To want revenge??

[thequickbrowndog]

Colleague absolutely favoured by manager as she is a massive brown noser. Works hard, work is her life etc

She is also a sly, backstabbing, tell tale.

I work part time, and when I'm not in she checks my work for any kind of mistake or for anything i haven't got around to doing yet and takes it straight to our manager, a twenty something year old desperate to get up the ladder. Me and colleague are in our 40's so manager hangs off her every word.

How do I deal with this? Colleague isn't actually doing anything wrong is she? Shitty as her behaviour is, management probably appreciate her snooping and tale telling.

I've come to the conclusion I can't stop her, but I can try to get one up on her somehow. Is this unreasonable behaviour??

Playgound mentality

This colleague is a sneak, she is also going above her pay grade, she has no right to be checking your work when it does not concern her.
This colleagues behaviour smacks of wanting to find things to get you into trouble. It sounds like harassment to me. Do you have a union to support you?
I would write everyone down, everything this interfering busybody has said and done and take out a grievance.I would also make sure I had a TU rep to support me in any discussion.
This bully has to be bought to task and your wet manager needs to be taken to task for listening to him/her. He also needs to do his job properly.

Are you sure your manager really loves her snooping and reporting back, and doesn't see it as a total waste of time? They might be being nice to her face, but has this actually resulted in any action being taken against you?

Well it depends.
If she's finding massive errors and helping the company, that's a good thing.
Wasting time trekking through already completed work to find minor issues, manager should be asking to stop.

Reading your op before your update, I wondered if you were a teacher.

Leave and find another school.

Honestly, believe me on this from bitter experience. It's not your colleague, indivudually. It'll be the culture of the school, right from the top, that encourages blame-finding and snitching.

Once, I'd never believe that there are schools where this is frowned on and no one does it. But there are, I work in one.

Don't stay. Don't take revenge. You'll just become like her and add to the toxic culture

Just do your job correctly then she won’t have anything to tittle tattle about and you won’t have to go tit for tat. She’ll be rattled and you’ll be settled. I’d leave it at that

I'd be making a formal complaint about bullying to be honest.