I want to kill my sister's pet mouse
I'm concerned. Why do you wanna kill an innocent pet?
Because it has been driving me crazy every time I see its eyes, it's blood-chilling
It's not okay to want to hurt or kill defenseless animals. Instead, you should talk to your parents about how your sister's mouse makes you feel and maybe they can come up with an arrangement so that you don't have to see the mouse.
You never hurt anyone. I will kill it.
If you kill it, then your sister will surely be upset and would resent you for a very long time, and it can take her years to forgive you. If you have your own pet and she kills it, then you would also feel very angry towards her, right?