Not much information, my friend. A little more would help. Is the broody caring for the other two? Where do you have her and the chicks? Are they protected from the other chickens? How old are the other chicks? Is this last chick a late hatch?
If the hen has abandoned the latest hatch, you might assume something is wrong with it. Hens cull chicks they know have genetic problems.
But you can try to raise the chick yourself, but it would be best to brood all the chicks together if you choose that route.
Yes, you need to show the chick and maybe the others, how to drink and eat.