Chick not right, butt smells?

[chickens really]

Thanks, everyone, for your input. I went over her bum very carefully, and there was no vent. That, plus the fact that she was very unhappy and would only get worse, I culled her. Never thought I'd see that situation, but . . . I'm sure stranger things have happened. Thanks again!

Best wishes with the other chicks. Definitely strange things can happen..

 

[casportpony]

Very sorry for you loss.

I the first picture you posted it looks like that yellow discharge (poop) is coming from the vent, so she *did* have a vent. In one of your later pictures I saw what looked like a scab on her belly button (umbilicus), so based on all of you pictures and your comments about the smell and bloated belly I think your chick had Mushy Chick Disease, aka Omphalitis

See more at: http://www.poultrydvm.com/condition/chick-yolk-sac-infection-omphalitissac-infection-omphalitis

 

[Wyorp Rock]

I agree with @casportpony I think she probably has an infection.
Still hard to tell if there is really a vent opening there or not. I could be in the circle below, I think I might see it there, but the swelling may be blocking it.
From your picture, to me, the scab below would be where the navel is and it doesn't look too good.
I'm very sorry.