Interfering with Hen hatched baby. Do or Don't?

[JennQuist]

I have a hen that hatched out 3 eggs a week ago and today I noticed one of the chicks doesn't seem to be thriving like the other 2. It is half the size and seems to want to stay under mother much more than the other 2. I do see a bump in its croup but it is not near the size as its siblings.
My question is, if I interfere and bring it in and verify that it is eating, drinking and discarding enough, will I be able to give it back to the hen in a day or two or will she reject it?

 

[TheChicken-nator]

She might reject it, she might not. I guess it just depends on the breed.

 

[JennQuist]

She might reject it, she might not. I guess it just depends on the breed.

She is a Bantum cross and is being a very good momma. She is protective of them, however she has been a pet for 9 years and does allow me to interact with them without attacking me. Since I just noticed it being off today and yesterday it was fine, would I be safe to wait until tomorrow and further assess its situation through the day, or would that be to late to step in?

Picture taken yesterday

 

[JennQuist]

Now it is Urgent. It seems this baby has not been eating or has gotten injured. I ended up bringing it in and when it takes a drink it acts as if it is ganging. After awhile of small drinks, which it is doing on its own, it seems to have thrown up all the water it drinks. Is this a clogged croup or did it eat something it wasn't suppose to? I do not feel it will make it, but anything anyone has got that I can try, I am willing.