However, friends and family of Sydney woman Jess Mudie, 22, are now struggling to come to terms with her life being cut devastatingly short.

Ms Mudie, who grew up in Wattle Grove in Sydney's south-west and lived in a Leichhardt share house, was one of five people killed when they were mown down in Melbourne's Bourke Street on Friday.

Ms Mudie, one of six siblings, had just enjoyed a summer holiday spent at the beach, having brunch with friends, celebrating Christmas with her family and ringing in the new year at Catalina restaurant in Rose Bay.

Last week, she was visiting Melbourne, where her older brother and his fiancee had recently moved, when she was struck while on the popular shopping strip.

Her twin sister Emily, whom Ms Mudie had previously described as her favourite person in the world, posted a smiling image of her sister online as the family released a statement on Sunday describing her as the "most badass" daughter and sister.

"We are constantly inspired by your love for everyone around you and the lengths you will go to for the people you love," her family said in the open letter.

"You are strong, beautiful, determined, always work hard to get what you want and never shy away from a challenge."

They described her as a "bright bubble of joy", who had a great sense of humour.

Holsworthy High School in south-west Sydney posted a tribute on Facebook to its former student.

"It is with much sadness and deepest sympathy that we convey the incomprehensible passing of ex-student Jessica Mudie," it said.

Ms Mudie left Allianz Insurance last February to take up a role as a consultant for national insurance broker Marsh.

The company's chief executive, Scott Leney, said: "We were shocked and saddened to learn of the death of our dear colleague. Although with us for just under a year, she had already won the admiration and friendship of those she worked with and had a bright future ahead of her."

A former colleague from Allianz said Ms Mudie had "ambition and drive beyond her time" and "always had a smile on her face".

She was known for bringing chocolate to work and always having her colleagues in stitches.

Ms Mudie loved having a long lunch with girlfriends, drinking cocktails in bars around Sydney and a gym session in between work.

Her best friend posted tributes online describing her as "the greatest best friend a girl could ask for" and "one of the biggest parts of my life".

A former flatmate posted: "Everyday I would get home and she would be there, eating junk food, bothering [flatmate] Reece... watching the same movie for the 10th time and then she would stop everything for a second and look at me with that smile, she always had that smile, the one that makes you feel like everything is ok. She was always so happy and full of life that it was contagious."

Four Melbourne residents also died as a result of Friday's carnage - father and husband Matthew Si, 33, Thalia Hakin, 10, a 25-year-old man and a baby boy thrown from a pram.

The alleged driver, Dimitrious "Jimmy" Gargasoulas, 26, was arrested at the scene after police shot him in the arm.

He was being followed by police after allegedly stabbing his brother in the arm about 2.15am on Friday, stealing the car, a red Commodore, from a family member and taking his girlfriend hostage in it.

He was seen performing "donuts" at a busy Flinders Street intersection before speeding down a Bourke Street Mall footpath and mowing down dozens of people.

As a nation struggles to process such a tragedy, a quote Ms Mudie posted to her Instagram recently stands out.

"Holding onto anger is like drinking poison and expecting the other person to die," it said.