There is no generational limit. However, a direct line of descent has to be documented back to an ancestor born or naturalized within the borders of what is now Canada.
Acadians in Louisiana have been successful in making claims back to the Le Grand Derangement / Expulsion by the British. They had meticulous records however.
Long form birth certificates that name parents and marriage certificates to show name changes would cover it.
Baptismal certificates can be used when there’s no civil registration of births. Civil registration began very late in several provinces of Canada. There’s more likely to be an Anglican or Roman Catholic baptismal record regardless of being Indigenous.
You may be able to find ship manifests and landing records in Family Search or Ancestry. Those list nationality — you would be looking for her to be a British subject domiciled in Canada at the time she landed in Australia.
Your great grandmother’s death certificate may have information that could be useful, as they usually state the place of birth. Newspaper death notices and obituaries can also be helpful as supporting information.
Lastly Canadian and US census records can be used as supporting information.