I continue to have fantasies about someone I hate
What kind of fantasy do you have?
I'm thinking of insulting her because I hate her. I want to get back at her.
You shouldn't hate people and shouldn't have fantasies about hurting them. Just move on and ignore them.
This is really going to screw her life and her mental.
I don't think it's really going to impact her if you are just fantasizing, which is good! I believe you need to just keep it to your thoughts, because openly hating can be quite harmful to her. Eventually you should be able to move on and do more productive things.