People are genuinely upset about this and I guess I can see why:

Apparently this lady, Sam Jones, is some sort of an outdoor/hunting influencer who was visiting Australia from Montana, so it's no wonder she handled that thing so easily.
From NPR:
Jones has since deleted the video and briefly made her Instagram private — but not before the clip spread across social media, angering Australian viewers, wildlife groups and top politicians.
...
In the days after Jones' video took off, calls grew for her to be deported and even banned from the country — one such online petition has gotten over 38,000 signatures. Home Affairs Minister Tony Burke said his office was reviewing the conditions of Jones' visa, to determine if she had violated it.
She did give back the baby wombat, but the internet still hates her:
Jones has since fled Australia and posted this lengthy note on her Instagram page:
Am I a villain?
Things, dear reader, are not as they seem.
Over holding a wombat, thousands threaten my life.
Let me be clear; these same people ought to understand the reality of Australia today. For the readers that are so angered by my mistaken attempt to help and that I am a hunter — do not be blind to your country.
Let's start with wombats —
The Australian government allows and permits the slaughter of wombats. Thousands each year are shot, poisoned to suffer, and trapped legally. Landowners rip up wombat burrows with heavy machinery, poison them with fumigation, and shoot them whenever they can. Quietly, of course, so as not to face the wrath that has come upon me.
Why, might you ask, do they kill them? Well, to feed you. The landowner is trying to survive, to raise you the lamb for your dinner table, the grapes for your wine, and the produce for your salads. Wombats get in the way of this, through putting their holes and tunnels across the land, creating hazard for livestock, and turning up the ground to eat roots. The wombat knows no better, as it too, is merely trying to survive.
Your government further spends tens of millions of taxpayer dollars annually to fly around in helicopters and shoot beautiful horses, deer, and pigs out its windows. A swift death is often not afforded to these animals. The Australian Government Department of Agriculture's research showed a percentage of animals end up painfully wounded and stated ‘Animal-welfare outcomes could be improved with a national-level standard operating procedure requiring helicopters to fly back over shot animals and repeatedly shoot animals in the head or thorax.' Sound kind to you?

P.S. Now check out our latest video 👇