Thank you very much for your query to Ireland Reaching Out. There are some records for the Termonmaguirk area dated to 1780. This is a householders list that can be found at the Representative Church Body Library GS 2/7/3/25. If you are lucky, you might find Sarah McNally's details or parent's details listed on this.
You could also check emigration records in Australia. Do you know the circumstances of their emigration?