A reporter for Time Out Chicago claims that Sarah was already signed with Elite model management before the show, and had seen her at casting calls. After Googling her, I found a link that had a supposedly pre-ANTM professional shot (the ANTM rules state you cannot be signed with a modeling firm in the last five years in order to compete, but they may be running out of contestants so this could've been changed).
See the full article: http://www.timeout.com/chicago/outandabout/?p=856
See an (alleged) pre-ANTM photo of Sarah at http://img477.imageshack.us/img477/9569/ld17243a2633437bfabe0c8wd3.jpg
See more modeling photos here (they look pre-ANTM, but I am unsure - also, isn't it in their contract to say they can't model until the show is done being broadcast?): http://www.fansofrealitytv.com/forums/americas-next-top-model-cycle-8/60925-sarah-cycle-8-a-7.html (scroll down a little)
and here: http://www.fansofrealitytv.com/forums/americas-next-top-model-cycle-8/60925-sarah-cycle-8-a-10.html (scroll down midway).
and she's also in these pics, which appeared in a beauty spread, I'm not sure which magazine though: http://img257.imageshack.us/my.php?image=sarah6ve6.jpg
and these ads: http://img184.imageshack.us/my.php?image=sarah3ya9.jpg
Hopefully these shots were taken after ANTM, because she didn't take quite as stunning shots on the show.