i once had a sister

Mitchell was born with asthma an incurable illness. For fourteen years of her life , she has fought a good battle. Even when the doctors thought she could not make it after an asthama attack, she always did ..for she had something or rather someone to comeback to... her little sister Trish
Mitchell had made a promise to her little sister that she will never give up, she will never leave.
But what happens when Mitchell's body no longer allow her to keep that promise?
How will the little girl , Trish cope without her sister!