STAR uses vocabulary in conext to score a level. The passages get more detailed and the vocabulary gets more difficult as the test progresses. Here are a detailed STAR link, it has some sample pics

http://www.godwinschools.org/documents/Star_tests.pdf

Grade Equivalent: 9.6
Your kid scored the same as an "average" 9th grader during the 6month of school

Percentile Rank: 99 (does this test even rank above the 99th?)
No scaled test will score above the 99th- Looking at my mountain of previous STARs. It seems that the 99th is earned around the 3.5grades up, benchmark.

Instructional Reading Level: 9.3
This is the level in which your DD scored atleast 85% proficient in understanding the vocabulary in context.

Zone of Proximal Development: 4.7-9.6 (seems like such a wide range to me--and why would it top out at her GE?)
I assume they do this do encourage kids to read a wide range of leveled books. Just because a kid reads at a 9th grade level does not mean that he/she can't increase her reading skills by reading lower level books.