How do I tell my Mother I'm quitting the family business?

My mother runs a real estate business and I've been working as a receptionist for her since October when I had to quit my job due to being severely mistreated. It was always meant to be a temporary thing, and she always told me when you're ready to leave just let me know when you're starting to look. There's been a really high turnover rate here. At times there would only be my mother, myself and one other employee. Since I've started she's fired two people here and two people have quit. I really want to leave. I need to branch out and regain my independence. I don't like having my mother write my paycheck. Our relationship is far too personal. I got called for a job interview today and I don't know how to tell her that I need to leave. I don't want her to resent me, but I'm just not made for the corporate lifestyle. I'm not happy here. In fact, I feel bored and understimulated. Any suggestions on how to have this conversation with her would be great.