In "Les diaboliques", how does Christina feign death?

The ending of Les diaboliques is ambiguous, and people have interpreted it in different ways. However, some of these interpretations fit better with the mood of the movie and suggestions it provides than others. I will suggest that the best explanation is that Christina does not feign her death: she really does die, as indeed she must to atone for willingness to commit a murder.

This raises the question of the child's story. Again, there are multiple possibilities; the simplest being the one adopted by the adults in the film: he lied about seeing Christina. But it is perhaps better, thematically, to see Christina as having been a persecuted soul who, after her physical death, continues on spiritually. One blog entry I encountered puts it like this:

There is no reason to think that Christina is physically alive at the end of the movie – that would merely be a stay of execution for her, and nothing in the film implies that she stages her death as Michel had staged his. Instead, the story of her reappearance and kindness to the boy convey an idea of Christina’s soul being preserved; she is free now from her own ruined body and her antagonists’ cruelty. For a religious martyr, that’s as good an ending as one is going to get.

A very thoughtful discussion of the meaning of the film can be found on Dennis Grunes' blog; he also believes that Christina dies. On the boy, he says

one must note at least in passing the symbolic weight of Christina’s name; sacrificial and redemptive for Michel and Nicole, Christina stores a bit of magic for the schoolboy whose vision of her “risen” is a deeply touching chord on which to close the film.

Watching the film again this past month, I have to disagree with the statement that “nothing in the film implies that she stages her death as Michel had staged his.” Just as Michel & Nicole cooked their scheme off-screen, there’s enough evidence to suggest that the retired detective, Alfred, and Christina could have cooked their own scheme off-screen as well. There is evidence of Alfred’s deus ex machina arriving moments after Christina’s death rather than before. The evidence of all those conversations between Alfred & Christina that Nicole was so visibly worried about but that not even the audience was party to. The evidence that what had been reasonably naturalistic acting of Vera’s Christina suddenly became so melodramatic at her death scene—even down to the rolling back of the eyes used by the earlier feigned death of Michel. There’s evidence of the cursory way in which dilettante Michel checked for a pulse. But the most explicit evidence might be from “slingshot boy” himself. He’s derided by the schoolmarms as a pathological liar, yet it is the adults who are in a constant state of prevarication (whether to cover their crimes or cover their assets). The scene when the boy is falsely accused of lying about the presence of the supposedly dead Michel is exactly the same as the final scene. There’s no reason that the film gives to believe that he was truthful the first time but not this time. I’m totally on board with the argument that the ending is intentionally ambiguous. But to then argue that there is only one interpretation supported by the film’s textual evidence isn’t itself supported by the film’s textual evidence.