In an essay, Georgia Rowe said that when she came round she thought: "I wish I'd never survived."
The 14-year-old and Neve Lafferty, 15, died in an apparent suicide pact, plunging more than 100ft from the Erskine Bridge in October 2009.
Georgia wrote an essay about being admitted to hospital after taking drugs and collapsing in October 2008, the inquiry heard.
In it, she said she felt she "belonged to nobody" after finally meeting her birth mother, whom she described as a schizophrenic alcoholic with drug problems.
The teenager was taken in by aunt Tanya Oliver at nine months old because her natural mother was not capable of caring for her.
In June 2008 her behaviour became so difficult social workers took her from her aunt's home in Sorn, Ayrshire, and put her in care in Hull, where she was originally from.
The inquiry heard she became increasingly wild in Hull, drinking alcohol, going missing, and on one occasion claiming to have had sex with a boy.
She also found her birth mother despite a court order banning contact between them.
The inquiry at Paisley Sheriff Court heard an essay that Georgia wrote in which she described how she felt after taking the overdose.
She wrote: "On that day things seemed to get out of control. I had taken an overdose of a number of unknown drugs. I was in my children's unit where I collapsed.
"Nothing was going right for me. I had met my real mam for the first time in 14 years and I felt like nobody was there to help me and support me.
"I felt like I belonged to nobody after meeting my mam. I always felt myself looking after her, me a 14-year-old girl looking after a 44-year-old. My mam could not look after herself."
The inquiry heard that when she moved to Hull, Georgia also started calling herself Terrie Oliver, which was her birth name, as opposed to 'Georgia', which her aunt had chosen.
Ms Oliver adopted two of her sister's other children but did not formally adopt Georgia.
The inquiry heard the girl seemed unhappy about this.
Jacqueline Postill, a foster carer who looked after Georgia in Hull, said in a written statement: "It came across to me she was deeply hurt that her brother and sister had been adopted and she had not.
"She said she asked Tanya and was told it was only a bit of paper. She also said both of them had been to private school but she had not."
Another foster carer, Rebecca Blampey, also in a written statement, said when she asked Georgia what sparked her wild behaviour, she blamed Ms Oliver.
Ms Oliver told the inquiry she had never thought the adoption was an issue for the girl. She also said Georgia had sat the entrance exams twice for Glasgow Academy, a private school, but had not got in.
She said: "It is no surprise to me she would blame me because I was not there. She would change depending on who she was speaking to."