The reason she was in the airlock was to protect her baby from the Cylons not to destroy him. Cally wanted to go somewhere where the Cylons couldn’t get to them. Obviously, she wasn’t thinking clearly at the time, but she wasn’t really wanting to killer either herself or Nicky. When Tory talked her down, she came out of her shock enough to realize what she had almost done, and she started apologizing.
I think, given time, we would have seen Cally’s love for the Chief overcome her hatred of all things Cylon.
What I find interesting is Tigh’s comment about Chief’s “Cylon-hating wife.” Not all that long ago, I’m thinking Tigh would have been passing Cally more ammunition to kill Cylons with. This shows me that Tigh has already “changed sides” so to speak. He’s thinking more like a Cylon than a human no matter what fancy speech he gave at the end of The-Episode-That-Shall-Not-Be-Named.
The last of the FF’ers to give up their humanity will be Anders, I’m thinking. Cally’s death is going to push the Chief over the edge.