As I make clear in my myth-debunking article Who was Mrs Garbutt of Cooyal? (recently updated), the said Mrs Garbutt was neither Fred’s “sister” nor his “mother”. In fact, “Mrs Garbutt” didn’t come into existence until Fred’s nephew, John Garbutt – who had also received a ticket-of-leave to Mudgee – managed to woo and wed the widowed heiress of Cooyal inn and station, Mrs Elizabeth Blackman nee Aldridge.
So how did this erroneous claim develop? See Who was Mrs Garbutt of Cooyal?