Here she seems to be doing a little impromptu hommage to the great Charlotte Greenwood, Queen of the Novelty High Kick Number:
I believe that her right to this moment in the spotlight was written into her contract at Fox, with a minimum of one per picture.
A true Greenwood aficionado watches her movies - in which she usually dithers away in support as an aunt, chaperone, or deceptively staid lady - for the moment in which the madness will break out. Tell-tale signs: a sweeping hostess gown, the handkerchief, and a certain glint in her eye that signifies Magic in the Making.
As for Tharp - she's heaven, of course, even if she only made a splash in one film, the fabulous Hair. I used to be a regular for her New York seasons, once upon a time.
And if I could do that with my leg...I probably wouldn't have time for blogging.