Living with an extremely rare condition called carnitine-acylcarnitine translocase deficiency (CACT), which doctors did not expect her to survive far beyond birth, the now 11-year-old has spent the past few years waiting for a surgery to have a port removed from her chest.

"She has it accessed once a month and she doesn't like it. They access it with a needle," Mollyjane's mum Jess Rothwell said.

"We've had to go through pain therapy, children's therapy, play therapy - years and years and years before we didn't have to wrap her up in a blanket to have it accessed.

"It's the longest standing port her surgeon has ever seen, they're normally in for 18 months, hers has been in nearly 11 years.

"When she's in catastrophic deterioration they can access that and give her the lifesaving drugs that she needs, but because it's been in so long she's now got veins in her hands they can use instead."

But due to Sydney's COVID-19 lockdown, the surgery has now been delayed - Ms Rothwell said probably for another year.

It comes as Mollyjane, perhaps better known as MJ, finishes up her year as an ambassador for Jeans for Genes.

Ms Rothwell took MJ to Hudsons Circus recently and began speaking with animal manager Mel Cook about her daughter's condition and role with Jeans for Genes, which raises money for children with genetic conditions.

It was then Ms Cook invited MJ to be part of the circus and spend a day training a horse in the ring before being a part of a live show the following week.

The circus is also giving MJ 10 family passes for the show that night

"Jess said how MJ loves animals and she'd love to run away with the circus, so I thought I'd let them come and meet the animals then the idea was hatched to let her be in the show," Ms Cook said. "It's a dream come true for her and she did really, really well."

"It's amazing," Ms Rothwell said. "When she found out she jumped and she flapped her little hands."

In the past year, MJ has managed to raise more than $35,000 for Jeans for Genes. Instead of presents for her birthday, the Adamstown girl held a raffle and asked people to donate to the cause.

Ms Rothwell said the chance to be in the circus was a lovely reward for MJ, but that her daughter didn't see it that way.

"She doesn't even really see it as a reward, she just sees it as an opportunity to help other people, but I see it as a reward for what she's been through and what she goes through everyday," Ms Rothwell said.

"Today on the way she got really emotional and said 'I've been given a really special opportunity'.

"Westmead says to us all the time, we will never know what tomorrow's going to bring. Tomorrow my life could be ripped out from underneath me, but I guess you just have to go and try and prove it wrong.

"She's a very individual unique little human, and some days when I don't feel like I can get up, she gives me that power to go you know what, life isn't that bad."

To donate to MJ's Jeans for Genes campaign, visit fundraise.jeansforgenes.org.au/fundraisers/miraclemollyjanesfight/my-own-idea