I am not entirely certain that I see the femme fatale characterization of women in Casablanca. I think that part of this might lie in the definition of how a femme fatale operates:
A femme fatale is a mysterious and seductive woman whose charms ensnare her lovers in bonds of irresistible desire, often leading them into compromising, dangerous, and deadly situations.
In the very basic form of the definition, the term brings out how women are able to manipulate men into a self- serving situations. It becomes one of the primary motivations of the filmmakers in Casablanca to undercut this from the start. Casablanca becomes a basic study in how self- interested driven situations is not present in the time period and in the context of the characters. The women reflect this. There is not really a female character who manipulates men into "compromising" situations, and certainly not through the activation of "irresistible desire." Ilsa is torn between her own love for Rick and the need to help her husband, Victor, to defeat the Nazis. I think that Ilsa is not out for any sense of self. This turns out to be part of her predicament. Even when she does act in her own interests in leaving Rick, it is to do so in helping a larger cause. Other female characters represent this. Yvonne is incapable of being a femme fatale when she breaks off her relationship with the Nazi officer to sing the French national anthem with a sense of spirit and zeal in the cafe, joining Victor Laszlo. Even the side character of Annina, the Bulgarian refugee, must use her "charms" in order to help her husband and she emigrate to the West, something that was averted through Rick's intervention. In the end, the film does a great job of suggesting that while the femme fatale characterization is present in Hollywood films, it is not something that Casablanca openly endorses.