We live on the 4th floor of our apartment building(technically the 5th
because it is a drive-under). The apt has a sliding door accessing a
balcony with a solid cinder-block rail - we're talking 8 inches thick
here and about 42 inches high.

Nothing is stacked within two feet of the rail and the balcony floor -
concrete - is about 6 feet deep from wall to edge. There is nowhere
for her to slide through and jump, but my concern is that 42 inches is
enough height to keep her off without having to screen the balcony in.

My neighbor is moving out and has a screen/frame he built himself that
he can install at our place at our request.

-Chris