How do you know when your mother is getting you a bunny?

You should just tell her: "Mom, I want a bunny." Then you can talk about it. I am sure that you will have to prove that you are able to take care of a bunny, and that you are responsible enough for a pet.

She still might say no if anyone in your family is allergic, or if there are regulations about having certain pets where you live, but starting a conversation about it will at least help you to know whether it is a possibility or not.