For it to be considered negligible homicide; the pills would had to have been given to her, if the bottle was labeled then as an adult, she chose to take them. Another scenario is if the pills were in a different bottle say an aspiring bottle instead of the labeled original bottle.
However, when it comes to children the laws are a little different.
One example would be to give a loaded handgun to a emotionally disturbed person, to leave a toxic substance within reach of a child and the child consumes it, to leave a handgun within easy access to a child, to leave a running car with a child in it and the child makes the car go and it kills someone, to leave a running car with the keys in it and someone steals the car and kills someone.
One rule of law is that it must be proven that you were grossly negligent in taking the necessary precautions or rather not taking them.