Hi Grace.
I'm assuming here that the Reta you are seeking info about is the daughter of Dora and Samuel McMillan, brother of Lancelot, etc., which is the family you have asked about previously?
According to the 1911, 1916, and 1921 censuses, this Reta was born in B.C. (British Columbia) as were several of her siblings. But the family was living in Manitoba at the time of the censuses.
If Reta remained in Manitoba, her marriage may have occurred after the dates available to the public due to privacy laws, which in the case of marriages is 80 years. Reta would still have been relatively young 80 years ago and could have married any time after the cutoff dates.
PB