Well according to their terms and definitions booklet it is:

"Any child dependent on another person, i.e. not in receipt of 'substantial' income in his or her own right. An adult has a legal responsibility either alone or jointly with another person for the day-to-day care of the child or in another person's care and is wholly or substantially in the other adult's care. Needs to satisfy the definition of an Australian resident."

I would say your letter definitely warrants a phone call to centrelink to query why she is not listed as a dependent child! Unless your DD is earning stacks of money for you? LOL.