Should I snitch on my co-worker or just let things be?

I am absolutely fed up with one of my co-workers. She is a nice person who will do just about anything for you, but her work ethic sucks! We are friends at work and go to lunch every now and then. We have also hung out outside of work once, so I would consider her a friend. I am the type of person who stays out of other people’s affairs at work, and I don’t want my name caught up in the middle of anything. However, this woman has driven me to the point of wanting to anonymously tell my supervisor about her behavior. There are eight people in my department and three of us (including her) get in at 7 a.m. She used to come and stand and my desk for 30 minutes to an hour EVERY morning and talk. This went on for about six months and I finally gave her the cold shoulder. I would talk to her with my back turned while I was typing on the computer. Either that or I’d be very short with her and she’d be forced to go away.