With Olivia, she is fronting TV ads for St John's annual appeal this week.
In Olivia's advertisement she gives a long litany of "thank-you's" for family events, the last a thank-you to St John "for my mum" as the pair embrace.
The appeal is so that the charity can buy 12 ambulances. They cost more than $200,000 each to put on the road with life-saving equipment, such as that which saved Mrs Wrenn.
St John CEO Peter Bradley said it was always looking for better ways to care for patients in New Zealand.
"We want to make sure that we are getting to patients faster, with the right care, first time."
St John also runs community programmes, including St John Youth, Safe Kids, Caring Caller, Friends of the Emergency Department, Outreach Therapy Pets and St John in Schools.
It recently ran a course at her children's Puketapu School, the first of its type in Hawke's Bay. It started with new entrants and ended with CPR for older students, part of a nationwide programme giving young people the skills and confidence to take action in medical emergencies. It was brought to Puketapu at the request of Mrs Wrenn.
"Because we live in the country a lot of other parents said if that happened to them, their children wouldn't know what to do," she said.
The appeal started Wednesday and runs until Sunday. To donate, call 0800 ST JOHN (0800 785 646), donate online at stjohnappeal.org.nz or at any ASB branch.