Martha in love with Edwina?
I know Martha and her brother had a few romps, but Martha seemed to also be in love with Edwina. The fantasy girl-on-girl threesome sequence at first seems it could be a male (clint's) fantasy, but turns out to be Martha's: she's dreaming of being kissed by, and kissing, Edwina. Also, in the end, the intensity to save Edwina: from death, and from going off with a man. Edwina was, before Clint "opened her up," per say, a virgin who despised men. I'm sure this worked well for Martha. Then Edwina fell for a man: and Martha ended that quickly.
I realize that Martha's reason for killing Clint was attributed to Clint not having sex with Martha, but... I think this is something to consider: That Martha loved Edwina.