I wonder if the reason you can't find a marriage record for Elizabeth and Benedict online is simply that these events are too recent to be made public. You as a descendant can probably apply to the official record-keepers and be allowed to obtain the records of Elizabeth and Benedict's marriage and about Elizabeth's passing -- for the regular fee.
That would be the case in my country (Canada). For my province, here's the records that are NOT put online:
Births less than 100 years ago
Marriages less than 80 years ago
Deaths less than 70 years ago
If either the party concerned or the immediate next of kin (spouse, children, parents, or siblings) are living, written proof of their consent to release the requested information is to be attached to the application.
Maybe someone here who researches in South Africa can tell us about the restrictions on recent records and where to apply for them if the applicant has an appropriate reason.
The regular fee is about $25 to $40 in most provinces of Canada. Again, someone who knows the fees in South Africa could maybe share that info.
Cheers
Shirlea