Sonia Kennedy told the jury she could not remember a number of details relating to the death of 21-month old Jordan Thompson, which happened more than 18 years ago.
Her brother Cecil Patrick Kennedy, 51, has pleaded not guilty to manslaughter over the toddler's death at Singleton in the NSW Hunter region on March 19, 2005.
Blood analysis detected high levels of an antidepressant Kennedy had been prescribed in the toddler's system, the District Court jury has heard.
Ms Kennedy told the court on Tuesday her brother's unit was clean and tidy, "for a male".
"It wasn't like my clean where I pull things apart and move furniture, he would just go around everything," she said, in reference to his vacuuming style.
But that's not what she told police in a November 2005 statement or a coronial investigation into the toddler's death in 2008.
She said Kennedy "regularly" vacuumed his unit, even going so far as to vacuum under the lounge and remove cushions.
Ms Kennedy was taken through a number of inconsistencies between her previous statements and evidence and what she said in court on Tuesday by crown prosecutor Kate Nightingale and denied making up evidence to assist her brother.
She told the jury she had previously attended Kennedy's unit after he tried to take his own life to find tablets on his bed, while telling an inquest in July 2008 they were all over the bed and floor.
It's been more than 18 years since the toddler's death and 15 years since the inquest into it.
Ms Kennedy blamed that delay for being unable to remember what she had said at different times over the years.
Ms Nightingale challenged Ms Kennedy's evidence on Tuesday that she had attended her brother's unit earlier on the day of the toddler's death, which she had not mentioned before.
Ms Kennedy said she probably had not mentioned it in her past statement, not thinking it important.
"It was a pretty momentous day wasn't it, a baby dying in your brother's unit?" Ms Nightingale said.
"That's not in any statement you've provided to police."
Ms Kennedy said she had told police but not included it in the statement she made about nine months after the toddler's death.
She said she attended the unit for a short period.
"I ended up leaving after Cecil got a bit angry with (the toddler's mother) ... because she'd hit the kid," Ms Kennedy told the court.
The police statement signed by Ms Kennedy says she had never seen the toddler and did not know what he looked like, which she could not remember saying.
Also not included in her statement was a reference to the toddler being fed in a high-chair.
Ms Kennedy told the jury she attended the unit hours before the boy's death, when his mother was feeding him an orangey substance, which he was spitting out.
She said the boy's mother was "squeezing his face, like getting angry" on Tuesday.
Ms Nightingale suggested she did not see that.
"You were making it up in an attempt to assist your brother weren't you?"
Ms Kennedy contended she was not making it up.
The trial continues.
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