I'm going to snitch on the girl whose house I clean
Why are you going to snitch on the girl whose house you clean?
I don't like her and I know that she doesn't like me either. I think she is crazy.
It's fine to snitch on the girl because she is in danger or has done something dangerous. However, you should avoid snitching just because you do not like her. Doing so will lead to negative consequences for you, including not being able to work in her house anymore.
I don't care. I'm going to the manager.
Before you go to the manager make sure you are doing the right thing. If they are in danger or have committed a crime, then it is okay to speak up. Just be careful before you do anything drastic.