Ok here's the situation. My aunt is really scared and doesn’t know what to do with my cousin. She has being running away, doing drugs (weed) stealing my aunts car (she is 15 and doesn’t know how to drive really dangerous) and making really bad choices (stealing, skip school, etc.). She tried to kill herself and run away etc.

My aunt loves her a lot. She is not a bad parent. She does not abuse her etc. this all began when she was going with this kid but they broke up but she keeps doing it. My aunt is really depressed and doesn't know what to do. My cousin had been in a suicide hospital to court and now she is receiving counseling by this nearby help center. I am really worried she is still doing this. We are worried she will get hurt or killed by an accident. Someone please help :/

Oh lord! I'm sorry to hear that. Your cousin already receiving counselling but I guess that's not helping. Your aunt's concern is obvious but you are there to keep her away from depression. You can help your aunt and tell her to be optimistic. I think your cousin need rehab. If possible she should be moved in good rehab. I think there is some court matter also going on. Before she do any more harm, your aunt must take some step which will ensure that she will not get hurt again.

Your aunt might try calling the police when she knows illegal things are going on. If this 15 yr old is allowed to continue with what she is doing, it will only get worse!
If she takes your aunt's car without permission, your aunt should call the police. Only your aunt can stop this. If she doesn't, it is called "enabling"; that is, letting her get away with doing it. It is only hurting her more. Good luck.

My Aunt does call the police and my cousin does this when my aunt is at work that's the thing

If you know she is driving anyone's vehicle or otherwise breaking the law you need to call the Police. FredG hit the nail on the head!

Your aunt isn't the only one who can make the call.

Where are the other responsible adults in your cousin's life?

If she was hospitalized and is in counselling there is probably little else that can be done - except putting her in jail and hoping that leads to another hospitalization and/or intervention.

And what do you think the OP can do/say to the aunt to keep her from being depressed? I have never found telling a depressed person to (basically) cheer up to be helpful.

"Your aunt's concern is obvious but you are there to keep her away from depression. you can help your aunt and tell her to be optimistic."

Call the cops, and Child Protective Services and have her removed from the house and put in a clinic for evaluation and a plan of treatment.

Your Aunt doesn't seem to be doing anything to help, other than asking you to help. How old are you? Are you an adult? If not, how does your Aunt expect you to help?

Your Aunt needs to stop feeling sorry for herself and start doing things to help her child. If that means calling the cops on this 15 year old, putting her in jail, then so be it. But it's up to the child's parents to do what needs to be done. If they can't, or won't, then the child needs to be removed from the home.