Let me try to reconstruct what might have happened. First, I can't figure out whether it's a he or she but since the general consensus is that the deceased is a she, I'll adopt that. She sat facing the mirror as she wrote her suicide note while smoking a cigarette to give her courage. Afterall, suicide it's not an easy thing. Then after writing she uses her right hand to bring the gun to the right side of her head which is the normal position for any suicide victim apart from those who who prefer putting the gun inside their mouths. While still facing the mirror and and involuntary clutching the cigarette, she closes her eyes and squeezes the trigger which accounts for the blood splatter on the wall. As she falls down, the stool gives way making her fall awkwardly to the right instead of the left which the velocity of the bullet would have pushed her to if she was sitting on a sturdy chair but the falling stool changes her falling position. She's dead by the time she hits the floor while the death grip makes her not to release the gun and the cigarette.