switch from electrolytes to chick vitamins..and/or give Poly-vi-sol liquid baby vitamins, Enfamil brand, no iron..give 3 drops on beak once a day for 3-4 days, then taper off for a week..
but try and get some chick vits..McMurrays has them..I think they call it Quik Chick..they also had a product called Gro-Gel for new chicks..
a teeny bit of sugar in the water might perk her up..
describe the droppings in detail..color and consistency..
have you checked the vent for pasting?
what's the temp you're keeping it at..also the others?
proper temp is 95 degrees F. for the first week..then 5 degrees less each week..
no drafts or wet..
a temp gauge in the brooder helps..also the behavior of the chicks.
is she trying to get near the heat light? or is she away from it? is the light placed so she can escape it if she gets too hot?
is she eating and drinking?
maybe she needs the chick feed crushed up smaller..some do..
some chicks are runts..sometimes called stunting syndrome..
with extra TLC some do ok..
some will remain weak..
I'm not saying this is the your chick's problem, just a possibility..
some chicks are slow starters..they need extra TLC.
if giving other foods then feed..keep a check on the crop..might need a little grit..
others might have more suggestions..