How about not her maiden name (father) but her mother's name- often the case in Scotland, or in the case of trying to lose your identity but holding onto a basic truth. So we need a Catherine born c1789 to a mother McNally/Macanally/Mackinulty etc
I have dissected the VDL Musters and Lists till I'msick of the sight of them!! may be missing something ,but don't think so. Have also cross checked all Catherines I could find in VDL 1814-1820 irrespective of surname, and they all seem accounted for.
I can find no single women free or convict in VDL called Catherine or McNally, born 1779 (1789 +10) or later that is not accounted for- so she must have arrived within a couple of years or so of the 1819 Muster when she appears as a wife of Thomas Ransom-
Of course, if she was not a Catherine at all, then we have a real problem
Remember the 1816 Cummins notice of taking John McNally and wife to VDL is bookended by the 1811 birth of John McNally to John McNally and Catherine, and by the 1819 Port Dalrymple Muster showing a male John McNally and a child John McNally but no wife McNally, while the Hobart Muster shows an unnamed Ransom wife, whoappears from nowhere. Yes,I am fixed in a groove, but I am holding onto facts, even if my interpretation may be wrong.
David