Context: Two girls are talking about something that happened to one of them (something started to grow in her back) and her mother told her that it's happening because her father is an angel. Her friend seems not to believe that story and the girl responds this:
I think she's saying here that, context here, what her mother said was a lie and she also thinks that it was a lie. Or the と思う is being redundant and she says she thinks that it was a lie.
I don't know if と思う is used for quotation apart from being used to express what you think.