Reading that “poem” in its entirety, he’s saying she had a penthouse apartment, went to Europe twice a year, had a Cadillac, and so on. How does anyone know it’s Mad. Dunham, when the name is spelled differently? Any evidence that Mad. Dunham went to Europe twice a year on shopping sprees and had a white Cadillac, apparenhtly a new one every year?
I would argue "creative license". Not everything must be true. Frank Davis said everything in his book "Sex Rebel" was based on his experience, but the story over all was not true. (He did use the name "Ann" though.) Frank was unquestionably a good writer. I bought his book "Livin' the blues" and it is quite well written and likewise an interesting story. I do think the references in his poem about Madeline are possibly linked to Madelyn Dunham, but I would regard the references to Matisse, penthouses, Broadway plays and Europe are more to be regarded as fanciful compliments meant to represent her dreams and desires. Possibly an effort to curry favor from her as a form of flattery. A Statement regarding her tastes perhaps.
Strike that. It was obviously meant to be insulting, more of a caricature.
Madeline had a white covertible as shown here:
‘Another high school friend, Maxine Box, remembered that they enjoyed getting rides in the old man’s WHITE CONVERTIBLE and that he was always ready and willing to drive them anywhere, wanting to be the life of the party.’ (Though Obama Had to Leave to Find Himself by David Maraniss
That poem is not about her. End of story.