As a New Zealander, I can safely say Meryl's accent was great
People who say her AUSTRALIAN accent was poor are completely misinformed. The real Lindy Chamberlain was never Australian, she was born in New Zealand lived there into her 20s I believe. That's why Meryl doesn't sound Australian, she sounds like a true New Zealander. She is actually spot on.
People should keep in mind that the disappearance occurred of Azaria over 30 years ago, the film itself is 25 years old and Australian/New Zealand accents were a lot stronger then. Now, the 'Aussie' drawl is less obvious as the accent today is mixed due to the increasing multiculturalism of the countries.