Try to find the spot where the photographer was standing.
How can this be, Elizabeth MacArthur nee Veale died 1850.
It may be another person? This Elizabeth is the daughter of James Macarthur and she married Arthur Onslow in 1867
Would it be Elizabeth Macarthur (1840-1911) on the left? I agree that would make her the grand-daughter of Elizabeth Veale Macarthur (1766-1850). If the photo was taken in 1858, it would make the later Elizabeth Macarthur-Onslow about 18 years of age.
Who, however, is Emily Macarthur, the older woman on the right? There is a striking physical resemblance to Elizabeth Veale Macarthur, with the strong aquiline nose and sardonic turn to the mouth. I am unable to locate an "Emily" in the family tree prior to 1858.
Elizabeth was the daughter of James Macarthur (1798-1867) who married Emily Stone, daughter of a Lombard Street banker. adb.anu.edu.au/biography/macarthur-james-2389 It seems Emily was Elizabeth's mother.