I got in contact with both Virgin Australia and Delta Airlines and here are their responses
Virgin Australia - "Hi Jessica, fares booked through Delta Air Lines, with a DL flight number, are entitled to Delta's baggage allowances, regardless of the flight's operating carrier."
and
Delta Airlines - "Thank you for contacting Delta Air Lines via Facebook.
Our records indicate another carrier for flights departing Melbourne,
Australia to Los Angeles, California. Please allow us to refer you to
Virgin Australia for the baggage fees requested. "
So now im totally confused they both are saying opposite things