I don't know the reason why I still exist!

It's about time dude, if she not open to you right now maybe there's some reason for her to do that. maybe she want to watch your reaction for first so she can make a decision for herself whether you are the right person to open her heart or not..

just give her your positive think always,, keep happy..

I think you are doing the best you can, by always being there for her...and one day, by some miracle, a word that may trigger her response, she will open up to you, as the old expression "still waters run deep"...and I admire you for recognizing that something is not quite right! Actually, remember you are only seeing into her family, what they want you to see....something serious, is troubling her....and I wonder if you should discuss this with the School Councillor, as possibly she is terribly desperate inside, and whatever is troubling her comes with some form of shame (that will denigrade her or her family) if outed! I would be so afraid, that there is some form of abuse, somewhere! This problem merits a lot of thought, and delicate handling! And congratulations to you for being so sensitive! Cheers!

I personally think it's best to leave her alone and support her secretly. She's at the rebellious stage and she probably thinks it's cool to be depressed about everything in life. It's pretty common for teenagers to think that way. Also, you may think there's nothing wrong in her life. The truth is, there may be something wrong (or something only she thinks is wrong). If she choose not to reveal, you shouldn't force her as it will only make her turn away from you more. All you can do is to give her space and just be there when she needs you.