She needs to be physically present in late August when auditions are being held and live in MD that year. She is also required to have private lessons in her instrument all year.
Placement is ranked and decided on performance during the audition. The top spots are often rotated during the year between a handful of the best players (concertmaster, assistance concertmaster, principal second and assistant principal second).
There is a wide range of skill among the violinists, due in part to their numbers in each orchestra. My similarly-aged child is concertmaster of their orchestra, has played since they were very little, and has two lessons a week with a professional soloist. It's their main extra-curricular. But the kids at the back of the second violins are not anywhere near that level, and probably started a few years ago, with one lesson a week at a relaxed teaching studio or music school.
At her age, I believe your child can register for both Chamber Strings (strings only, 4-6th grade) and Young Artists (first full orchestra, 6-8th grade). This gives her a chance of being accepted into Chamber if she doesn't get into Young Artists.
Click on the appropriate links on this page to see the solo, scale, sight-reading and excerpt requirements:
https://mcyo.org/?page_id=161
The solo is mostly to determine her musicality and expression, and maybe show off advanced technique. The scales and excerpts need to be as perfect as possible. Follow every single dynamic, fingering and bow marking to the letter, since they are looking for students who can follow directions. The excerpts will be played in full during that same year. She can practice sight-reading by herself or with her teacher. Usually the sight-reading is just a single line.