What I know of her parents, or who we presume are her parents, are from her brother, Peter McEwan, born 9 Feb 1912, who married the sister of Vivian Albert Sinnamon (Daisy's first husband), who was Vera Jane Sinnamon. There is a book on the Omakau/Ophir area that says that Peter and Daisy are siblings. If that is correct, then their parents were Peter McEwan, who married Mary Jane White in 1902.
Is your Peter McEWAN of Manorburn Dam father of W McEWAN the jockey from Central Otago ?
This Peter McEWAN seems to be married to a prominent member of the Poolburn - Moa Creek Women's Division of Federated Farmers
That would probably mean that the Manorburn Dam is what I know as the Upper Manorburn Dam accessed from Poolburn. Poolburn is over the Raggedy range from Ophir
The Poolburn - Moa Creek area is part of the wider Ida Valley District where 4 SINNAMONs were baptised in 1910
Allen Darcey SINNAMON
Louisa Rachel SINNAMON
Albert Vivian SINNAMON
Ruben Elizabeth SINNAMON
These appear to be part of your family of interest as they are connected with McBREENS by marriage at the nearby Parish of Lauder of which Omakau was probably a part in 1902
SINNAMON Allan Darcey 22y married McBREEN Margaret 19y on 16 Apr 1902
There is a second SINNAMON-McBREEN marriage recorded at Ida Valley 5 years later
SINNAMON Albert 22y married McBREEN Louisa 19y 1 Jul 1907
from Presbyterian Archives
http://www.archives.presbyterian.org.nzThe connection seems to be established by the report of the Poolburn - Moa Creek WDFF in the Dunstan times of 3 Aug 1936
"Presentations were made to three recently married junior members, Mrs V. Sinnamon, (nee D. McEwan), Mrs S Simons, (nee M. Harrex), and .Mrs B. Turner, (nee I. L. Harrex)."
https://paperspast.natlib.govt.nz/newspapers/dunstan-times/1936/8/3/5I have not found other related McEWANs in the Presbyterian Archives though there are a number of Lauder and Ida valley marriages connected with McBREENs
One of these related names DUNDASS features in the Ida Valley District History by Judy BECK
Signal
ps What is the title of your Ophir - Omakau (Manuherikia) source ?