Probably the work of Philip de László, Florence Kling Harding, c. 1923
Son of a Budapest tailor, he reinvented himself as Philip de Laslo, married into the incredibly rich Guiness family and painted royalty as well as Pope Leo XIII. Click on this link to see a portfolio of his regal subjects and to read about the life of this astonishingly talented painter. Curiously, this portrait isn't mentioned at all, hence my use of the words, probably the work of. Compare how lovingly he has posed his subject, fixing her hair and giving her a lovely complexion, all the while obscuring her bulky frame with soft and silky material.
Florence appears to be wearing the same clothes and casting the same look as in the photo below. Even though Genthe was a superbly talented photographer, capable of the Ferguson portrait, below, the painting creates an image of a First Lady that these photographs totally lack in style or technique. The beefy upper arm suggests to me that there was precious little effort made to pose Florence in a sympathetic way.
We know that this is a photo taken by Arnold Genthe, one of the early famous photographers, about whom I've written in Analog Photography at its Best. Contrast this photo with an earlier and sublime portrait of actress Elsie Ferguson, below.