My daughter was born with sadness?

My teenage daughter (17 yrs) doesn't like being around our family at all. She doesn't eat with us at the same table and always sits in the living room to eat. She doesn't come out of her room and enjoy any time with us at all, it's like she lives in her room. She doesn't go out with us to parties and would rather stay home alone. Sometimes I wonder where my oldest daughter is. Ever since she was young she would never play with her siblings and would always prefer to stay alone by her self. She's really quite and only talks when she has to talk. I've often heard her crying in her sleep and just crying in the middle of the night. I hear her whisper and talk her self to sleep. I always hear her say that everything is her fault and all the blame is always on her, she says that no matter what she says or thinks, she's always the wrong one and she attempted to do suicide but I found the note before she could go anywhere. I don't know what to do, she's just so isolated and always seem to be sad. Ever since she was young, she has been known as the cry baby of the family since she cries so much even if you aren't yelling at her. She would always hold everything in and break down at one time; she never wanted to share or talk about anything. Could it just be that she's too soft hearted?