Colin Mandy SC told the Victorian Supreme Court jury Patterson would have stayed at home and accepted medical treatment immediately if she was really pretending.
Instead, Patterson took her son on an hours-long drive the day after the lunch and she initially resisted doctor's advice when presenting to hospital two days later.
"If you're pretending to be sick, you would say to the medical staff, 'hook me up, pump me full of drugs'," Mr Mandy told the jury.
The barrister began his third day of closing arguments on Thursday as he tried to convince jurors Patterson is innocent of three counts of murder and one count of attempted murder.
Prosecutors allege Patterson, 50, intentionally poisoned her former in-laws Don and Gail Patterson, Gail's sister Heather and Heather's husband Ian Wilkinson.
Don, Gail and Heather all died after consuming the beef Wellington lunch on July 29, 2023, served by Patterson at her home in regional Victoria, while Ian survived.
Mr Mandy argued Patterson was also unwell after the lunch, although she was not as sick as her lunch guests.
He pointed to her hospital blood test results which showed she had low potassium, elevated haemoglobin and elevated fibrinogen.
Intensive care specialist Andrew Bersten's evidence was those results were consistent with stress in the body relating to a diarrhoeal illness, Mr Mandy told the jury.
He rejected the prosecutor's assertion Patterson had those levels because of psychological stress.
"That is an unfair way of categorising the evidence," Mr Mandy said.
Mr Mandy also claimed prosecutors inaccurately portrayed phone tower data from when Patterson discharged herself from Leongatha Hospital.
Patterson left the emergency department shortly after 8am on July 31, two days after the lunch, and did not return to the hospital for more than an hour.
Prosecutors alleged her phone connected to the Outtrim base station in that time period, which was consistent with Patterson driving along the Bass Highway.
Mr Mandy urged the jury to reject that claim, saying the evidence showed Patterson's phone connected to the Outtrim base station for less than three minutes.
He said that was consistent with Patterson remaining in her Leongatha home and her mobile connecting to a base station with a better connection.
Mr Mandy also maintained Patterson did not conceal her actual mobile phone from detectives, saying the allegation she set up "dummy phone" was merely a prosecution theory.
He told the jury Patterson's usual phone had been damaged and that was why she had a new phone at the time of the search warrant.
Mr Mandy reminded the jury Patterson was not being judged for her actions and the lies she told after the meal.
"There are all sorts of reasons why an innocent person can engage in that conduct," the barrister said.
"Erin got into the witness box and told you she did those things because she panicked when confronted by the terrible realisation that her actions had caused the illnesses of the people that she loved."
