Elaine is paraphrasing a line from certain movie. She was doing it out of frustration to mock the lady who was blabbering and kept calling her fiancé "baby".
It's a reference to the 1988 movie A Cry in the Dark starring Meryl Streep, who uses a New Zealand/Australian accent, as this movie was based on a true story.
The gist of that true story is:
Azaria Chamberlain (11 June 1980 – 17 August 1980) was an Australian 2-month-old baby girl who was killed by a dingo on the night of 17 August 1980 on a family camping trip to Uluru (also known as Ayers Rock) in the Northern Territory.... Her parents, Lindy and Michael Chamberlain, reported that she had been taken from their tent by a dingo.
And apparently that incident did become a bit popular after Meryl Streep's movie. In the film, Streep's character, upon discovering her daughter missing, cries out, "The dingo took my baby!" See that scene here:
As you see, it was a tragic incident. But at the party that lady was annoying Elaine by referring to her fiancé as "baby" and with an even more annoying accent when Elaine was already bored. So Elain took a shot at her and blurted out "Maybe the dingo ate your baby!" followed by an evil smile.