Make sure you are not putting sugar or anything else in the water. Clean off her butt so she doesn't get pasty butt. I'll try and find more info for you.
Here's a post about how I treated my weak chick:
https://www.backyardchickens.com/forum/viewtopic.php?id=293742
Here's some really good info from threehorses:
With my babies, I will often give them a prepared probiotic (Probios powder or an avian specific probiotic) on their second day of eating. Babies come without enough good bacteria in their gut. Mother Nature provides for that by giving chicks and amazing curiosity which often leads them to peck their mother's vent and droppings. That's how they naturally acquire both good and bad bacteria from their mom. Because their mom is healthy, the good outnumber the bad and colonize the gut faster and more thoroughly. Remember that otherwise their gut is pretty much free real estate! If the bad got to it first, they could just as easily take over. Because my babies aren't hen-raised, I give that insurance to my chicks that the good will outnumber the bad. I do probiotics up to weekly through the growth period, and then occassionally thereafter even to adults to re-innoculate their guts.
They will NOT grow dependent on probiotics for gut bacteria if you feed them. They will just benefit from them.
The bacteria help your bird actually absorb their food by finishing the digestion process on what the gizzard mechanically breaks down. They also help control pathogens by literal competition for that same 'real estate' of the gut!
So... when babies "might have' coccidiosis, I always start them on probiotics. If I see pasty-vent, I use probiotics daily until it either goes away, or until other symptoms present. If I see diarrhea in chicks (not just the occassional cecel chocolate-pudding droppings) I give probiotics first if the chicks are all active, eating, not sleeping too much. If the babies at all get lethargic, then I treat with Corid AND probiotics. I continue probiotics every other day after medication for 2 weeks. Then I go back to "occasionally", etc.
Moi again--she also recommends that you separate any weak chicks out, like I did.