Sounds encouraging, keep a close eye on her and hopefully the vits will help and you won't have to go to antibiotics since they can cause their own set of problems..
How is she acting this morning? Oh I know no way to keep the water clean we just have to hope a little dirt mixed in with the vitamins will still help.
Save a chick has vitamins and electrolytes in it I believe so yes start her on some asap. Keep a close watch on her but remember if you keep her inside where it's warm which is a good idea if they are sick but you'll have to slowly acclimate her back into the cool or cold weather. Is she eating...