Serial baby killer Kathleen Folbigg has given evidence for the first time about her personal diaries, defending them as evidence of her frustrations as a mother and not admissions of guilt.

Folbigg was jailed for at least 25 years in 2003 after she was found guilty of killing her four babies – Caleb, Patrick, Sarah and Laura – in the decade from 1989.

The 51-year-old did not testify at her trial but teared up at times when she faced the Coroners Court in Sydney on Monday.

Six of her diaries taken from the 10 to 11-year period, in which her four children died, are before the inquiry. Up to five others are unaccounted for.

In questioning Folbigg, barrister Chris Maxwell QC for the Office of the Director of Public Prosecutions said: “I’m suggesting you got rid of the diaries because there was significantly incriminating material in those diaries. What do you say to that?”

“I don’t agree with that at all,” Folbigg replied.

Mr Maxwell cited an October 1997 entry, four years after Sarah’s death, in which Folbigg wrote: “I think I am more patient with Laura. I take the time to figure what is wrong now instead of just snapping my cog”.

He said: “What I’m suggesting to you is that there’s a distinction between feeling frustrated and ‘snapping your cog’. They’re different concepts is the point I’m trying to put to you. What do you say to that?”

Folbigg replied: “At the time I didn’t differentiate between them. If I was slightly frustrated that equalled me being out of control in some fashion, which equalled me snapping my cog.”

“There was no differentiation for me,” she said.

Mr Maxwell suggested Folbigg had used the phrase “as a mitigating term for something that you had done to Sarah in order to stop her living”.

“No, I won’t agree with that at all,” she replied.

The diaries obtained by police also include comments such as Laura being “a fairly good-natured baby” which “saved her from the fate of her siblings”.

“I think she was warned,” Folbigg wrote in December 1997. Laura died in March 1999.

“With Sarah all I wanted was her to shut up, and one day she did,” Folbigg wrote in November 1997, adding in a January 1998 entry that Sarah “left, with a bit of help”.

Folbigg said she would write in her diaries as a release or to vent and rather than talking to her then-husband, Craig Folbigg, who fathered the four children.

Mr Folbigg sat in the public gallery on Monday and is legally represented.

The inquiry continues.

-AAP