I am currently living in my parent's extra house with my sister, but moving out soon because we don't get along. I'd rather pay rent elsewhere than continue living there for free.

My company is hiring a marketing coordinator, my sister applies. (Company is aware that she is my sister, and a few know that we don't get along.) She is technically qualified for the job, and may well be appropriate for the position. I assumed that if my coworkers had any intent of contacting her, they would notify me first. Without notifying me, the hiring manager schedules a call/interview with my sister.

This puts me in a very awkward position. I dread the idea of working with her, it stresses me out just thinking about it. I envision my joy in my work dissolving away if I have to sit 15 feet away from her every day, listen to her at lunch, be forced to interact with her in a professional setting, etc.

Does anybody have any advice on how to respond? Should I notify the hiring manager about my concerns? Should I directly advise against hiring her? Is it unethical or unfair to "sabotage" her chances by notifying them of how it would affect me (reverse-nepotism)?