I grew an orange sapling from a seed 8 years ago. Should I transplant her to a different pot? Her current pot is 6"x5"x21/2". Her soil is home made: Finley chopped dry bark, sand, kitty litter, and soil. My question is when should I transplant her to a new pot and fresh, properly prepared bonsai soil, and what type of pot should I be looking for? I want to keep her minture. Can I use the same pot?

Depends on what your plan is. You're on a bonsai forum, so I guess you want to make a bonsai out of it in the future?