Fluid in the ears can be seen when the doctor checks her ears so if her ears have looked normal with various physicals I doubt that is what has happened.
My two year old also covers his ears and says "Ow" with loud or unpleasant sounds. If your daughter can also repeat what you have said that means that she can hear the words just fine, too. And since she has started to repeat your words in the last three months that seems to be a big improvement to me.
It certainly won't hurt to have her evaluated, though.