Isn't this factually incorrect?

It's said in the movie she wrote a play about Josephine which was a flop.
NO - she wrote a book, "Every Night Josephine" (her real first book) and it sold decently.

She and Irving are shown arriving at the premiere of Valley of the Dolls...on dry land. She hated it (true), but stops complaining and seems to feel better when Irving tells her it's making a fortune.

She did go to a premiere - on an ocean liner. She did hate it, called it a piece of (crap) and she walked off the ship in the middle of the showing. Her only acknowledgement about making any money from it was "well, I did take the money after all."

I saw the best minds of my generation destroyed by madness, starving hysterical naked.