Kathleen Simango, who wrote this postcard, was from Africa. In 1923, she and her husband, Kamba Simango, went on a fundraising tour in America for missionary work in Africa. I don't know how or when Sibyl came to know Kathleen and Kamba, or whether they influenced her in her choice to go to Africa as a missionary.
Sibyl had met up with the Simangos in Portugal - see:
In that letter, there's no mention of a possible trip to England by Kathleen. She died in London of appendicitis the following month on July 20, 1924. And that's probably the reason that Sibyl kept this postcard. And then, later, I guess she gave it to Kay.
I thought you might like something fresh to dream about + so I am sending you this pleasant gentleman. How’s the tatting [???], any cleaner? Yours with love Kathleen
When I googled on Gbangbama Devil, I got the exact same picture. I got the following from another website
https://www.agefotostock.com/
Gbangbama Devils (Native Jesters). Sierra Leone has a rich cultural history, with a strong presence of traditional local mascots, who (to this day) appear in the form of devils. These devils are often highly decorated and represent an important part of local traditional culture and society.