I have had luck blending up the crumbles a little to make them smaller for the babies to eat! This has never happened to me in the past, but one of the new babies is smaller than the others and would just peck at the crumbles instead of eating them, and I guessed they were probably to big for her tiny beak so I blended them up for like literally only 3 seconds in my magic bullet and she has no trouble anymore!
It's good that she ate some of the yolk. Maybe try mixing that with crumbles to make a mushy consistency? Perhaps she has low energy. That's great you are providing electrolytes, but perhaps try sugar water? I've never made it myself but I've heard from folks on here that it "revives" their lethargic chicks. I believe it's 1 tsp sugar for a quart waterer. This is all I can think of, but I hope it helps and that your baby eats by herself soon