You could use the Super B-Complex, but I would limit the days to around 3 since it also has the added electrolyte ingredients.
Nutritional yeast sprinkled on the food may be a better option. What we're aiming for is to get B2(Riboflavin) into her for leg support. The other B-Vitamins are also...
Glad the mat is helping.
If the legs seem weak, then give the chick 1/4 tablet B-Complex daily. You can find human B-Complex at Walmart in the vitamin aisle.
For tiny chicks, I just dissolve the tablet piece in a tiny bit of water, then give the chicks drops of the vitamin water several...