I think the OP wanted to know if it was OK for a nine year old to use a ladies room....YES it is perfectly OK & anyone that disagrees is being totally irresponsible in their answer.
Then what is the point of this thread ? To stir the pot ? imho, I think the OP was just looking for strokes that she is a good mom and not actually interested in any dissenting opinions.
But then again, I've been wrong before....