Miss Kingsley paid her visit to the West Coast in 1893. Like all who travelled in West Africa, she heard of the woman missionary who lived alone among the wild Okoyong, and made a point of going up to see her. Miss Slessor welcomed so capable and earnest a worker, "She gave me," says Miss Kingsley, "some of the pleasantest days of my life." In some respects these two brilliant women were much akin, though they were poles asunder in regard to their outlook on spiritual verities. They had long discussions on religious subjects, and would sit up late beating over such questions as the immortality of the soul. Miss Kingsley was profoundly impressed. "I would give anything to possess your beliefs," she said wistfully, "but I can't, I can't; when God made me He must have left out the part that one believes with."

Nevertheless Miss Slessor said that for all her beliefs and unbeliefs she was one of the most truly Christian women she had ever met. On her return to England Miss Kingsley spoke often of her in terms of affection and admiration, and acknowledged to friends that she had done her much spiritual good. Mary, on her part, poured into her possession all her treasures of knowledge concerning the fetish ideas and practices of the natives, and probably none knew more about these matters than she. Most missionaries confess that they never get to the back of the negro mind, and one who worked in a neighbouring field once said that after nineteen years' careful study he had yet to master the intricacies of native superstition. The information that Mary supplied was therefore of great value, and much of it was utilised in Miss Kingsley's books. In Travels in West Africa she gives the following considered view of the missionary:

This very wonderful lady has been eighteen years in Calabar; for the last six or seven living entirely alone, as far as white folks go, in a clearing in the forest near to one of the principal villages of the Okoyong district, and ruling as a veritable white chief over the entire district. Her great abilities, both physical and intellectual, have given her among the savage tribe a unique position, and won her, from white and black who know her, a profound esteem. Her knowledge of the native, his language, his ways of thought, his diseases, his difficulties, and all that is his, is extraordinary, and the amount of good she has done, no man can fully estimate. Okoyong, when she went there alone—living in the native houses while she built, with the assistance of the natives, her present house—was a district regarded with fear by the Duke and Creek Town natives, and practically unknown to Europeans. It was given, as most of the surrounding districts still are, to killing at funerals, ordeal by poison, and perpetual internecine wars. Many of these evil customs she has stamped out, and Okoyong rarely gives trouble to its nominal rulers, the Consuls, in Old Calabar, and trade passes freely through it down to the seaports. This instance of what one white can do would give many important lessons in West Coast administration and development. Only the sort of man Miss Slessor represents is rare. There are but few who have the same power of resisting the malarial climate, and of acquiring the language and an insight into the negro mind, so perhaps after all it is no great wonder that Miss Slessor stands alone, as she certainly does.

With all her robust ability Miss Kingsley's mental range was curiously narrow. She wrote strongly against Protestant missionary aims and methods in West Africa, her views being entirely opposed to those of the White Woman of Okoyong, who had a much greater right to speak on the subject. But the latter, nevertheless, loved her, and when the news of her death came, some years later, she was plunged into grief. "The world held not many so brave and so noble," she wrote. "Life feels very cold and seems grey and sunless." Hearing of a proposed memorial to the intrepid traveller she sent a guinea as her mite towards it.