Johnnie Mae Rice (Graham) was the pianist from the day the International Sweethearts of Rhythm formed in 1937, ’til they disbanded in 1949, yet somehow there is very little biographical information for her to be found online. There is a video clip in which she takes one 12 bar chorus with the Sweethearts which is tasteful, light, and just right. Its apparent from her presence even in this video clip that she really embodied the music and was the perfect player for this setting. (Listen on for some great playing by tenor saxophonist Vi Burnside, as well.)
The only bit I could find which did more than merely list Ms. Rice-Graham’s name was this quote from the Wikipedia article which includes a little of Johnnie’s description of life on the road with the Sweethearts.”…as a racially mixed band, they defied the Jim Crow laws of the South. Because of the Jim Crow laws in the southern states of the former Confederacy, during the time that the Sweethearts toured the U.S., the band’s pianist Johnnie Rice mentions in the 1980 Kansas City Women’s Jazz Festival interview that “[They] practically lived on the bus, using it for music rehearsals and regular school classes, arithmetic and everything.” Despite being stars around the country, when the band traveled in the South, all of the members ate and slept in the bus because of the segregation laws that prevented them from using restaurants and hotels.” 
In 2011, at age 97, Johnnie appeared in a panel discussion honoring the legacy of the International Sweethearts of Rhythm at the Smithsonian’s celebration for Jazz Appreciation Month.  Although she remained quietly seated throughout the discussion, according to Lolita Thomas, who provided service to Ms. Rice-Graham during her visit to Washington DC for the Smithsonian celebration, she was very excited to have been “recognized for her valuable contribution to such an important milestone in the history of women.”  She died only a few months later.
 Wikipedia contributors, “International Sweethearts of Rhythm,” Wikipedia, The Free Encyclopedia,https://en.wikipedia.org/w/index.php?title=International_Sweethearts_of_Rhythm&oldid=874806334 (accessed January 18, 2019).
 Megan Mayhew Bergman. “The International Sweethearts of Rhythm.” (Oxford American. Issue 75, Winter 2011. https://www.oxfordamerican.org/magazine/item/297-the-international-sweethearts-of-rhythm).
 Lolita K. Thomas. Comment in “Johnnie Mae Graham Obituary.” August 8, 2011. https://www.legacy.com/obituaries/name/johnnie-graham-obituary?pid=152840341&view=guestbook