I was searching for Sandra, Lady Howard, and this is said to be her at her first wedding.
The thing that struck me is that the tiara she's wearing appears to be Lady Delia Spencer's tiara that was recently sold.
Daily Mail Article.
Lady Peel, sadly, died without children. Her sister, Lady Margaret Spencer, had a son, Robin Douglas-Home, Sandra Paul's first husband. It appears that she loaned the tiara to her nephew's bride for her wedding, but it would be interesting that it would appear that Lady Margaret didn't receive tiara upon her wedding.