It's possible you're thinking of another actress or a different kind of apocalyptic scenario. Can you provide any more information? For example:
* Other details about the movie: What genre is it? When did you see it? Are there any other actors you remember?
* The exact scenario: Is it a nuclear explosion, or a different type of disaster?
* Specific details about the plot: What happens after the explosion? Who are the main characters?
With more information, I can help you find the movie you're looking for!