As you ask Comments on your proposals :
Cane capiteuse : usually "capiteux" or "capiteuse" is much more used for things, not for beings. Very often it applies to perfumes/wines. It means with a very strong taste/smell that fill in your sense of taste/smell.
Cane cramoisie : in french this adjective means "to become purple" and also "deep red near to purple" in french the lunar crimson bat could eventually have been translated to "chauve souris cramoisie" but "chauve douris pourpre" was really prettier (wow i really wrote that about crimson bat ? ).
Cane captivante : "captivante" in french that adjective usually applies to ideas and or exchanges you have with someone. So in french you usually do not express a physical attirance for a man/woman with that adjective but rather an intellectual/smartness one.
I hope i m not too hard with those answers !
I find your question very difficult.
Maybe but it is a little from slang you ll have :
Cane canneuse : in french "caner" is a figurative verb to say "to die" so in this way i think it really matches the "femme fatale" alliteration. But i m not sure everybody knows that verb.
Cane capitale : find it weird but choose to share. Capitale is an adjective that means "leading to death sentence" in french. But the problem is that "capitale" is also the main city of a country, paris for france.
Cane canon : "canon" is a familiar adjective for a very pretty man/woman. A "canon" is also a "cannon". But it lacks that idea of something really lethal as with "fatale" and also of a really sophisticated woman.
I do not find anything else. Do not hesitate ti comment those proposals.
Hope you fill find something.