My understanding is that graphic artists begin with a human model as a starting point for creating a main character (e.g. Jamil Mullen for Alyx Vance in HL-2).
Who was the human model for Kate Walker?
I wouldn't want to see that person, that's for sure. :)
Seriously, I believe she was designed "out of mind" and together with April Ryan from The Longest Journey form two of the most ugly designed female characters. However, there is a lot of inner beauty in them to compensate.
I'm going back and forth between the games looking at screenshots, and I can't figure out why you say they are two of the most ugly designed female characters...granted, the artists in both games don't seem to do a great job with the human figure - it's like they spent it all elsewhere and didn't care too much about the characters. But they don't seem ugly to me, not more so than many other games. What am I missing about them?