Not that this is a particularly dense film, I still managed to get a bit confused regarding the way Marilyn was treated in the movie. Like everyone (except Larry) would be telling her what an amazing actress she was, but when we see the takes, she's practically screaming her lines. Were they all to her out of pity or to help her confidence or something? Even Paula? What was the point? Meanwhile, I actually don't remember her being that bad of an actress from the movie's I've seen. She certainly didn't constantly look uncomfortable and scream her lines as portrayed in this.
There were several reasons that everyone constantly showered her with praise:
1) Whenever anyone failed to flatter her, she had a meltdown and refused to film for hours. They just wanted to get her in front of the camera and do some work, so they were always trying to build up her confidence.
2) It's a traditional Hollywood way to treat actors, showering them with insincere praise.
3) Some of the praise wasn't insincere! When Paula Strasberg told Marilyn that she was the greatest actress in the history of film, she really believed it.
I never believed that Marilyn was all that good, myself. She had a lot of star quality, true, but she didn't give many good performances and didn't have much range.
They said that in the final years of her life her attitude was getting worse and worse because her mental state was deteriorating. She always delivered in the end hence why she seemed to have given a good portrayal in the Prince and the Showgirl but as we saw from the film, off screen it took her a while to get it right.