C.M.
In my opinion this will teache her the resolution when things are sad. My daughter was like this a few months ago and she is still empathetic, but not to the extreme she was then. Remember that when children learn something new (even feelings) they take it to the extreme until the learn how to moderate it. I think that as long as you are reassuring her it is the perfect way to teach her the moderation that she needs. Do not discourage the empathy, I think that we have too little of that in our culture today.