Its entirely up to you, its just that exptressing is such a hassle when you don't have to. A little water won't start off allergies or anything if you wanted to try it.
If you had to leave her for a couple of hours or so she could be fed before you went and would probably be OK until you got back. In an emergency she would take something, she could be spoon fed or something.
Or as the ifc said "if you're not there its not your problem . Not sure how I feel about that philosophy mind.