Dillwynia prison governor Shari Martin said she lodged at least two intelligence reports on Astill and kept the documentation in a locked safe in her office, but did not tell her superior of the sexual assault allegations.
A special commission of inquiry into what staff and prison management knew about Astill's offending heard at least 15 female inmates spoke to correctional officer Kim Wilson about the abuse in November 2015.
A report was filed by Ms Wilson, but Ms Martin claimed to have no memory of the meeting, or the report.
Astill was jailed for a maximum of 23 years this year for abusing his position and assaulting women at the correctional centre, on the outskirts of Sydney, for several years until his suspension in 2019.
Under questioning, Ms Martin admitted she was aware of the allegations made against Astill, and conceded she recognised he was a problem within the prison for a significant period of time.
"I didn't know what to do with him," she told the inquiry on Thursday.
Ms Martin said she had a telephone conversation with her custodial corrections director, Hamish Shearer.
"I was desperate and needed his assistance," she said.
"I needed something done."
Ms Martin said she told Mr Shearer: "I don't know what to do with this man."
But she was unable to describe the specific actions she believed needed to be taken.
Commissioner Peter McClellan questioned whether Ms Martin could have better managed Astill's roster to ensure minimal exposure to inmates, or taken steps to have him relocated.
"Yes, I could," she replied.
Ms Martin denied allegations that she called correctional officer Jean Dolly a "f***ing troublemaker" for filing multiple reports on Astill's misconduct within the prison.
She also denied telling Ms Dolly to "get the f*** out of my office", before adding: "You will not be f***ing taking an AVO against one of my best officers."
Ms Martin insisted she did her job "to the best of my ability at the time".
"I would not not report incidents to my superior," she said.
The inquiry continues, with a final report is to be handed down in December.