How to ask my mom about going to a suicide prevention walk?

There's a suicide prevention/ awareness walk in August in my town ,and I really want to go. I've had some pretty close experiences with suicide, both with friends and myself. I even have someone who would LOVE to walk with me, but I'm not sure if my mom will go for the idea. How do I bring it up to her? I want her to realize that I'm serious, and that it would be a GOOD thing for me to do this!