Marilyn Monroe struggled to overcome a stutter, and her breathy, airy vocal styling was arrived at with the aid of a speech therapist as a tool to help her overcome her stutter.
It mostly worked, though her stutter did come back with a vengeance in her later years, and some speculated that the added stress of its return was her undoing.
Regardless, the net effect of that breathy tone gave a kind of whispered edge to certain words which made her accent sound similar at times to a Spanish accent.
In this 1955 radio interview, listen to how she responds to the interviewer at around the 40 second mark when she says, “Don’t let ’em fool you. I’m not.”
Marilyn Monroe had a pretty unique accent that was a product of both the era and her speech therapy. Ana de Armas sounds fine to me.