Jill Stevenson was clearly upset after being handed a bundle of documents social workers had compiled on Kimberley Hainey.
Ms Stevenson was given the case papers for the first time yesterday - five years after she should have seen them.
She told an inquiry into little Declan Hainey's death that she would have dealt with his heroin addict mum differently if she'd been given the reports while working with her.
Referring to the reports compiled just before and just after Declan was born, Ms Stevenson said: "I'm upset at reading it and not knowing it.
"If I'd known about her history dating back to 2005, I would not have been comfortable with the situation at all."
The documents referred to Hainey's drug problems, family relationships and mental health issues, which saw her admitted to psychiatric hospital twice in 2007 - the year before Declan was born.
Ms Stevenson, who dealt with Hainey around the time of Declan's first birthday in April 2009, was never given the key paperwork, which shaped the involvement the social work department and other agencies had with Hainey and her son.
She said yesterday: "What I've gathered from reading them is that at the initial assessment there were some interesting presenting issues.
"Post-birth there were less presenting issues and there appears to be a period of stability however it was extremely short lived."
The inquiry heard that the period of stability referred to also included Hainey's relationship with her mum. At one point they had only been on speaking terms for four days when it was noted the relationship was stable.
Hainey was jailed for a minimum of 15 years for murdering him but her conviction was quashed and she was released last April on appeal.
The inquiry, at Paisley Sheriff Court, continues.