"My mother was the organist and I sang The Old Rugged Cross and forgot the words so sang the first verse four times.''
Della, a mezzo soprano, has sung major roles throughout the world in most of the leading opera companies.
However, tiring of endless travel, she decided four years ago to coach young opera singers instead in London.
"My experience means that I can help young singers with all the dynamics, difficulties and intricacies of singing an operatic role.''
Young Christchurch baritone Angus Simmons sang the famous Count's aria from The Marriage of Figaro with aplomb and dignity.
Though Della said he had sung well she insisted he revisit the dynamics of the role and took him through the aria again step-by-step.
"And you must remember he is an arrogant man and walks like this," she said.
Her elderly audience loved it and though opera wasn't everyone's musical passion they appreciated the vocal differences at the close of the master lesson.
Residents Betty Ross and Jennifer Clarke were thrilled.
"We loved it. So very interesting,'' Jennifer said.
Betty said; "All music is beautiful and we're so lucky they came to us."