Concerned that one if my chickens is not eating well.

[HudspethsHens]

My Ameraucana Chicken seems to be a lot smaller than the others her age and she is not very interested in treats. I did picked her up today and hand feed her some meal worms, which she loved but was more interested in getting down. I also think she is the one who’s poop is like black tar. Any thoughts about her would be welcome. Here are a few pictures.

 

[dawg53]

Black tar type feces can mean several things: Internal bleeding, type of feed she's eating, or eating some types of dirt that cause black tar feces or eating wood ash which can cause black tar feces. There might be other examples but what I mentioned is just off the top of my head.
I dont believe it's internal bleeding with your hen since she's acting like a chicken should, maybe just a bit skittish.
As far as her size goes, it might be genetic or where she's located in the pecking order. Perhaps other birds that are higher up in the pecking order wont let her eat or chase her away from the feeder. The solution is to add another feeder away from the original feeder.
It's best to observe their behavior at feeding times, especially in the mornings, then you'll know for sure.