In fact, the issue isn't that the female voiceover is rare; it's that, as I refer to it on my website, "the hardboiled film noir paradigm" denied its possibility. Here are paragraphs from my write-up for MOSS ROSE in Film Noir: The Encyclopedia.
"The longstanding view of film noir as having a male subject, with the female relegated to being an object (obstacle or enigma) in relation to the male, is unlikely to remain dominant. New perspectives about women in film noir will have to emerge, if for no other reason than to assess leading female characters in movies that are now acknowledged as film noirs but once were defined as not film noir.
For example, film noir has been contrasted with “female gothic” (and related but not identical terms like “period film” and “gaslight melodrama”). The prime reason female gothic has been called different from film noir is its focus on a woman instead of a man. Moss Rose suggests one way the inclusion of women’s film noirs (whether set in the gas-lit past or the atomic present) should lead to changes in the traditional description of film noir. From the start and throughout the film until the end, Rose narrates her story. Although the voice-over may generally be male, Moss Rose shows film noir doesn’t preclude, due to any inherent conventions, female control of the story."
Thus, added to Don's entries: Peggy Cummins in MOSS ROSE.
And let's not forget that, although Joan Fontaine doesn't voiceover throughout REBECCA, her voiceover opens and closes the film, in 1940!
I think the strong supportive internet responses to my two-part posts for Noir of the Week on The Blackboard about RAW DEAL (August 23, 2012) entitle me to re-post my analysis: