Hey Oscar, thank you sooooo much. I'd never heard that song before. Why, oh why wasn't this woman a star?
There were a lot of these golden voices of the late 50's-70's that were never stars. Most of it had to do with what record label they were signed to. Motown was obviously the biggest label and those artists got the most promotion. Some of these other artists made bigger splashes in the UK than they did the in the USA because they toured more in the UK.
Mitty's biggest record label was Chess Records of Chicago, IL (which is now owned by Universal Music Group), who also recorded the likes of Muddy Waters, Howlin' Wolf, John Lee Hooker, Willie Dixon, and Chuck Berry. Chess Records was a big company back then, but I don't think they promoted the women as heavily as the men
You might know that The Rolling Stones song "2120 South Michigan Avenue" is about the physical address to Chess Records, where they made a recording on their first US tour in 1964.