I was watching Prometheus again (I don't know why either) and Charlize Theron's performance sure has me thinking she is a robot. Could be she's just playing it as a cold, detached human, but her mannerism, tone of voice, etc. could certainly be interpreted either way.
When Janek straight up asks her if she is a robot, she doesn't deny it, just suggests that they have sex. Can androids not have sex in the Alien universe?
At one point, while speaking with Peter Weyland, she calls him father and does it in a voice very reminiscent of how Roy Batty says it to Tyrell in Blade Runner.
I suppose you could say she took the name Vickers to avoid the look that she was riding her father's coattails, but it is somewhat odd that her last name isn't Weyland if she was his daughter (she doesn't strike me as the type who would care what others thought about how she got to her level.)
Is Vickers an android?
I'm not steeped in Alien lore outside the core movies, so if it is definitively answered in a book or comic, please let me know.