This repeats some of the evidence from yesterday and adds a few more details.
Mrs Stewart's sister, Wendy Bellamy-Lee, was asked by the prosecution: "Would it be fair to say that you always had concerns about the cause of Diane's death?"
She replied: "Definitely. There was an element of suspicion because Ian had been on his own," and said that she called the coroner's office days after her sister's death to ask for more information.
She said she "did not think it was fitting to ask a grieving husband how his wife had died".
Ms Bellamy-Lee said she felt she needed to let Stewart know she had contacted the coroner, and she called him.
"He was really, really cross with me," she said. "He was so cross with me. Then I felt really bad that I had done that and I had to tell him.
"I felt really bad that I thought I had upset him because he was so cross with me."
Reading from her witness statement, she said Stewart told her that calling the coroner was "inexcusable".
"I think he put the phone down on me, very blunt," she said.
Ms Bellamy-Lee clasped her hands together and trembled while giving her evidence.
She said her sister had collapsed at the checkouts at a supermarket in 1992, but said it "wasn't a major thing".
"Diane wasn't an epileptic person," she said. "She didn't suffer from epileptic fits throughout her life.
"Diane was fantastic. She was my older sister. She was the sister that I looked up to."
She added that Diane was three years older than her, and described her as "strong, healthy and active".
Asked if she could remember Stewart's demeanour when she saw him in the days after Diane's death, she said: "Just very calm."
Murder trial told Ian Stewart was 'so cross' after sister-in-law called coroner