(OOC: She has to climb up to do that for the somatic components, so...)
*As Obscurity climbs up, the eye shoots at her and misses. She quickly casts Protection from Evil and moves to the side while the eye is recoiling from the shot. She casts Blink as the eye shoots at her again, though she dodges again too. Now comes the tricky part!*
(OOC: The tightrope is 150 feet long and 1 inch wide. She can cross it in four rounds if she moves at half speed and takes her time and never fails a check. Since she's moving straight into the eye, it never has to reaim, so that's three chances to be shot. If she takes a -5, she can make it in 2 rounds if she makes all her checks and get shot at only once. A fall here will bring her down several levels, but that's irrelevant because it will also bring her to negative HP)