Telling therapist about homocidal ideation?

I'm 16 and there's one girl that I always think about killing. The girl is also 16 and we used to be friends like 3 years ago but due to her pathological lying and her other Psychopathic traits we can't get along.

I also have some antisocial traits so I'm usually able to see through her when others can't and she hates me for that, and I hate her because I can see through her.

Anyways I have homocidal ideation towards this girl. It has been going on now for about a year and it seems to get stronger and stronger. Now it is at the point where I have planned her death multiple times.

The only thing that is keeping me from doing it is the fact that if I get caught I will go to prison.

My mom and friend knows that I want to kill her. Hell, even the girl knows I want to kill her. My friend always tells me that I am crazy, and today my mom told me that I need to tell my councilor.

Now to be honest I don't see anything wrong with these thoughts. Yea they are probably not necissarily "healthy" but I feel that they are completely justified considering the fact that I see the girl as a waste of oxygen and as a danger to society.

My councilor is a social worker through juvenile justice. I've had her since 8th grade when I got charged for vandalism and disorderly. I like her a lot, but I'm not trying to get thrown in the looney bin.

But knowing my mother she will probably tell my councilor about these thoughts regardless of me not wanting her to. I'm not scared of getting sent to the looney bin but Its not exactly how I had imagined spending my summer.

So anyway given the information do you think that my councilor would have to report me? What would happen if she did? If i don't want to get sent to the looney bin do you think it would be best to downplay the thoughts and make them not sound as bad?