Maybe you can put food and water up there for her, then JUST before hatch snatch them away to the incubator? I can't think of how to keep the babies from falling, maybe a low hardware cloth ring around her nest until all the eggs are hatched, then assist them to the ground?
The crows will definitely get the babies, sorry. Maybe when she flies down to eat, place a board under the nest and try to move the whole nest to a safer location? Keep an eye on the eggs until you're sure she'll resume sitting on the new location, there's a chance that she may not, but if you...