Chyler Leigh, who plays Meredith's half-sister Lexie Grey, was first introduced at the very end of last season. Many fans already don't like her character much as she is already getting in the way of the Meredith and Derek relationship.

Leigh's original contract stipulated that she would appear in 13 episodes. But it seems that as writers and the show's creator, Shonda Rhimes, are mapping the upcoming season, they are thinking to have her stick around as a permanent fixture.


http://www.tvsquad.com/2007/07/06/chyler-leigh-may-become-a-regular-on-greys-anatomy/