There is no reliable evidence that Matilda Whitbread was born in England. It is highly likely that she was not Isaac Whitbread's daughter, as she was raised to believe. However there are some family members who are keen to sanitise their family history.
The original manifest for the "Charles Kerr" did not include anyone in steerage, including the Whitbreads. A copy may be viewed in the State Library of South Australia. The passenger list quoted as a reference here refers to a compilation by the late Diane Cummings from other sources. It listed the Whitbread children as Elizabeth, William Charles and Matilda. There is no primary record indicating that William had a second given name. There is a marriage record for Charles Whitbread in St Stephen's Church of England Marriage Register at Willunga, South Australia on 1 Feb 1856. His sister Sarah Ann was also married on that day. She was born on the voyage to Australia in May 1840, as per her baptism record on 10 Feb 1842 in Holy Trinity Church, Adelaide.
The Application for Assisted Passage to South Australia, dated 18 Feb 1840, is for a 31yo male, 33yo female, male children aged 6y and 2y, and a female child aged 11y. The baptism register for Tidcombe, Wiltshire indicates that Isaac and Emma/Amy Whitebread's son Charles was baptised on 9 Feb 1834 and William on 6 Aug 1837. Thus is can be concluded that William and Charles are different people.
Matilda was baptised in Holy Trinity Church, Adelaide on 7 Aug 1845, the same day as her mother remarried John Wilson. The baptism register has the notation "posthumous child" and a date of birth 2 Apr 1845. Her parents were stated as David Whitbread (no other record has been found of a person of that name) and Emma Whitbread. Her marriage took place on 11 Jul 1866, and the certificate indicates that her birthplace was Adelaide, South Australia and she was aged 22 years. Her death occurred on 27 Oct 1924. The death certificate states her age as 80y, birthplace Adelaide.
The owner of the record is aware of these facts and has chosen to ignore them.