Advice regarding Discretion

About 6 years ago, when I was starting high school, I told my mother that I was interested in possibly joining a particular sorority in college. My mother shrugged it off and never paid any attention to it until a few years ago when some family members brought this sorority up to my mother and was giving her the heads up that she may have to help me with the financial aspect of Sorority Life. After that, my mother COULD NOT KEEP HER MOUTH SHUT!! She told everybody, from my entire family, the neighbors, the people at our church....just anybody with ears. I told my mom that I was no longer interested just so she would stopped telling everybody. For the past couple years, I've been working my butt off so that I can take care of the financial aspect myself and wouldn't have to ask my mother. But now, my mother is telling everybody that she knows of in this sorority about my interests. I understand that my mother may feel her intentions are good, but I've told her that she needs to keep my interests between me and her. How do I stress the importance of discretion to my mother without appearing rude to her? Is there anything I could say so that she realizes that her help isn't needed? (I know this is fairly long...sorry) Any help is appreciated