How long can a person with Alzheimer's live without eating and only drinking a little water if they weigh only 110 lbs?

It depends on the age of the person. One can go without eating for up to two weeks or a little more, but not without water. Also, if the kidneys are shutting down then the person will not be able to pass the fluids in their urine and need a catheter to drain it. Again, age is everything. Only God knows when the person is going to pass on. I've seen miracles where a person looks like they are going to pass away at any time and without warning bounce back.