Sorry that she was hurt again.
Separating them with Martha was a good idea.
You can give her drops of electrolytes, sugar water (1tsp sugar to 1 cup water) or something like Poultry Nutri-Drench if you need too.
Tiny syringes are very good to use. I usually push out 1 drop at a time, hold the drop against the beak and let it sort of roll around the edge of the beak, the chick will usually take the drop in. It's slow and tedious but will work.
Another method is dip a qtip in your electrolytes/sugar water, etc. Basically same concept, press the qtip lightly against the side of the beak to get a drop of liquid to roll out and let the chick take it in.
Were you providing multiple feed stations for the flock? Sometimes that can be helpful as well. I usually set up several if I have small chicks with the flock. The whole flock gets chick starter or all flock crumbles, that way feed is the same for everyone and it minimizes hogging/aggression over feed. Just make oyster shell available as usual.
Just a question - is Martha tending to Little Chick or is she ignoring her? Basically, checking to see if Mama may be rejecting her for some reason. That can happen. You will know soon enough.