When you take your own life you take a chance that you will not be with the Lord. God gave us free will. I hope that girl is in Heaven with God but I would not bet my life savings on it. Physical age almost always coincides with spiritual maturity and a child who is suffering is more likely predisposed to make a bad choice.
As a christian I believe you are obligated to embrace the death that God sends you. Some deaths are easier than others and only God knows why.
Whatever you might think of your own life, your position on this matter shows you have not really ever suffered. You speak frivolously, as one who has only read books. IMO, if you keep it up, God will send you an opportunity to learn compassion. My advice therefore, FWIW, is that you make the effort to learn that lesson before God breaks your pride.
Physical age almost always coincides with spiritual maturity...
In my experience, that is not true at all.