My Little Pony: Friendship is Magic - Image #199,228

@TARNunit9
That's one of the great things about Valve's 'silent protagonist' set-up. It really lets the player insert whatever personality they want into the character. Everyone's Chell is a little different.
(On topic, I like to imagine GlaDos screaming "BIRD! BIRD! BIRD!" whenever Scootaloo enters.)