I am so sorry to hear about your kitty and daughter
How old is your sick kitten? Are giving human baby formula, Similac? If so, that is intended for humans, not kittens, please stop immediately, KRM is formulated for kittens.
What nasal drops are you giving your kitten? I have never heard of any for cats.
Were the antibiotics from the vet? The most common and very safe for cats is clavamox.
Your cat may have the herpes virus which can come back, usually when the cat is stressed. Supportive care is the normal course of action, lots of fluids and quality food and quiet time.