I think that people forgive flaws in males more easily than they do females.
Out of this year's bunch of females, the two sisters are the most inoffensive and "sweet". For female characters, it's the "sweet" and "ditzy" character archetype that the general public seems to warm to most easily. Generally, I feel that we're more likely to hold a woman's negative character traits more strongly against her than we would do with a man. The good thing about a vote to save is that women who provoke a reaction have a better chance of breaking the mould and surviving against these character types.
If there was to be a female winner, Katie and Lucy are likely. They have that "Aleisha" factor. I don't think they will get there in the end though - we're most likely getting another male winner.