This is definitely a call for help. She's purposely pushing her boundaries with the intent to have someone save her. This is not something malicious to hurt you though. She's suffering from depression and she needs help. Luckily for her it is fairly difficult to kill yourself with Zoloft and most of the newer antidepressants but there is no doubt damage may occur. How old is your friend? If she's living with her parent's, they must be told or either a trusted family friend or school counsellor. If she's over 18, still seek the help of other's in her family and friend's. Again, these were not attempts at suicide, they were cries for help. That doesn't mean she won't go a step further and actually die the next time.
She does need to see her doctor or psychiatrist. I do believe she should be in the hospital if only for her protection. She may have to stay for a week or so. If she admits herself, she can usually decide when she can leave. (if she's eighteen). She's obviously turned to you for help and as hard as it is, you do need to do something. Do some research on the computer about depression and suicide. You'll learn a lot.
It has gone too far already honey. Talk to her, listen to her, and above all else, step in and stop her from doing this or like the previous caller said, call an ambulance.
This is so very difficult and I wish the best for you and your friend.