Ah, of course it was designed for her father.

I still think she's human. Although she is described as cold, she actually shows quite a lot of emotion throughout the movie, such as anger with her father's quest for immortality and how she panics before she dies. It seems she also has sex with Janek. While travelling, she cryo-sleeps with the rest of the human crew (David doesn't sleep) and when waking up (she was the first to wake up), she tries to "exercise" off the cryo-nausea .. and again, she's annoyed with her father's want of a son (David). If she was an android, would she really have such feelings?

.. But I also believe the movie and her character was purposely made ambiguous to make you wonder, a bit like one could suspect Deckard was a replicant in Blade Runner