How to deal with my 15 year old?

Hello everyone, I am fairly new here. I am desperate for help so I have posted this in many other websites.

I am a single father from France of a wonderful 15 year old girl. We adopted her. My wife and I had the chance of bringing her home when she was only 6 months old. Unfortunately for us, her mother and I have been separated since her 14th month. She just left and never came back.

Basically, I have been living alone with my daughter since that time.  I try my best to be the best single parent I can be. I give her all my attention and I introduce her to as many things I as can. She is a very smart, curious and happy child. Well at least, she was. Everything changed when my grandmother died when she was six.

Since that day, she has been a very pessimistic and ‘dark’ child. The worst is that the death of my grandmother did not affect her at all. She just got very fascinated with death. At first, she just looked like any other child asking questions about where ‘mamie’ went and if she will ever come back. But as she grew, her curious comments on death became a true obsession and I am worried.

My daughter and I are still very close and she does not hide things from me. She comes to me whenever she needs me – it can be for a hug or for a legit advice. But when she talks about death, I feel extremely uncomfortable. Her questions are usually very frightening to hear from a young girl. The worst was when she was 11 and she told she wanted to look at someone in the eyes while they die. She still has this wish.  

My daughter does not wish to kill but to see how death works. I can understand the curiosity behind it but it’s really frightening me. She is so willing to see how it works that she had tried to commit suicide twice already. She was badly injured the second time. And both times she filmed the attempts. She also frequently runs away but she now allows me to come with her. Last year, I bought a little house in the countryside so we can “run away” to there.  

Besides death related stuff, she likes burning papers and hitting things. She has a little box full of lighters (she has about 6 or 7) and brings at least two with her, wherever she is. And whatever she feels, she always ends up hitting a hard object with her first.

Only I seem to see something wrong with her. She seems happy. However she is just doing things that are odds. And she has been doing those since a fairly young age. Besides, she is very sociable and is appreciated by her friends and our family members. She never misbehaves in school and she is a straight A student.

I do not understand what can be wrong with her. I love her so much! But something is just odd … Before, when I look at her in the eyes it used to be of a sparkly green color. It was so alive! But now, it is dead. There are no emotions whatsoever. Her bright smile is enough to foul anyone into believing that she is still the bubbly baby of the family. I just don’t see it in her eyes anymore.

What can I do? Should I even be worried? She also does not want to go see a psychiatrist. She says she does not want to believe that there is something wrong with her.

Thank you in advance for your help.