(Didn’t want to have an overly long title, sorry if it’s a little vague)
Georgia Tech allows one teacher letter of recommendation. The teacher that knows me best (from a great deal of working together for Science Olympiad, as I’m a captain of the team), has however 1) never actually taught me in a class, and 2) is currently semi-retired (after the past school year) and moved to another state (contacting her shouldn’t be a problem though).
Are either of these important factors I should consider?
Colleges look at teacher recommendations to get insight into how a student functions in an academic classroom setting. Per the school website GA Tech specifically recommends that you ask a teacher of an academic subject (for example, English, math, science, social science, or foreign language) to complete the form as instructed. http://admission.gatech.edu/freshman/recommendations Follow their instructions and get a teacher who has had you as a student for a core academic subject to write the LOR.
Some schools allow supplemental LORs from people who know you outside of a traditional classroom setting so if you apply to any of those then you certainly can ask the advisor for Science Olympiad. The fact that the teacher is semi-retired (or even retired) makes no difference.