like another poster said, i don't think that will be the case because jenna-louise was cast as a companion and THEN filmed the dalek episode. the previous people (eve, freema, karen) were cast as random people (gwyneth, cyber girl, soothsayer) and THEN cast as main characters (gwen, martha, amy.) they already knew she was going to be a companion when they filmed the daleks.

edit: oops lol i guess everyone's on the same page.