I personally don’t think that moving this thread and attaching it to the other Buckland thread would be too helpful.
See what Sarah advises, but I think you could just post on that thread that you are looking for a Buckland or Heard descendant who went to Australia and see if anyone has any information that might help. Maybe leave this DNA query here on the DNA board?

Have you or your contacts traced all the descendants of Charles Buckland and Mary Hearne? I think you might need to work on constructing family trees for these people and their descendants to see if you can find their connection to Elizabeth Smith.
I know almost nothing about mtDNA tracing, and I am sure someone will be able to advise further, but as the mtDNA follows the female line, could the rumoured aboriginal component be from her father?

Have you considered an autosomal DNA test? They are a lot more popular than mtDNA tests so you might find you get more matches that with your mtDNA test.
Do you have any evidence that these Bucklands were Romany or Convicts? If you do, it might give a starting point for further research.
Whereabouts in Australia did Elizabeth live/die?