The girl was bitten at a property near Walgett, in the state's north, on the afternoon of February 5 and was transferred to the local hospital to receive anti-venom.
She was airlifted to Sydney Children's Hospital and placed on life support but was transferred back to Walgett Hospital after her condition deteriorated, and she died on Saturday, police say.
The little girl's death has prompted NSW Ambulance to issue a timely reminder to be wary of snakes as the warmer months continue.
Tips include calling Triple Zero immediately after a snake bite and to always check clothing and items left outside before picking them up.
If bitten on a limb, apply a pressure immobilisation bandage until help arrives, but not so tight it will cut off circulation.
For bites on other parts of the body, direct and firm pressure should be applied with hands, and the patient must be kept still, NSW Ambulance say.