Sassi died in a Melbourne hospital after developing Haemolytic-uraemic syndrome, known as HUS, seven weeks after a trip to a petting zoo where she held, rode and petted animals, the Salter family said in a GoFundMe post.
The family of four said they had "been living a nightmare" after the toddler spent six weeks in intensive care battling kidney failure and a brain injury.
"We've lost our darling girl," the family wrote.
"Sassi was strong. Surprising many at each corner. She was courageous and a fighter. She fought so hard. We all fought so hard."
While the little girl didn't show pathological signs of the syndrome, her family believes it was likely caused by a bacterial infection, possibly contracted from the farm.
It can occur when a strain of the E.Coli bacteria (STEC) releases toxins into the body, inflaming blood vessels and causing clots which can cause gastro symptoms and damage the kidneys and other organs.
The bacteria is commonly found in the gut of several types of farm animals, including cattle.
Children under five years of age are at greatest risk of developing HUS.
"The torture as a parent of not being able to console your own child, not through lack of trying anything and everything you possibly can but because they are truly inconsolable," the family wrote.
More than $50,000 has been raised to support the family, which they said "allowed us to spend every second at Sassi's side".
"It helped us keep her comfortable. It will help honour her."
The family called on the community to prioritise hand hygiene by carrying hand sanitiser and washing fruit and vegetables.
"Please donate blood if you're in a position to do so. This is a lifeline for many critically ill people."
The STEC bacteria can be passed on to humans by eating undercooked beef, drinking unpasteurised milk, drinking or swimming in contaminated water and contact with farm animals.
It can also be found in lettuce, spinach, sprouts, salami and fruit juices.
Symptoms include bloody diarrhoea, dehydration, seizures, jaundice and hypertension.
About 1000 STEC infections are reported in Australia each year, of which a very small number of these people develop HUS, the Australian Centre for Disease Control says.
