Melt butter in a large dutch oven on medium heat. Add onion and sauté until soft but not browned, about 3-4 minutes.
Stir in flour and sauté another minute.
Add chicken broth, water, carrots, garlic, celery, brown rice, salt, and chicken thighs. Cover and simmer 20 minutes.
Add wild rice mix along with seasoning packet and mushrooms. Simmer on low, covered 25 minutes, stirring occasionally.
Remove chicken from pot and shred with two forks. Return to pot and add yogurt and more water if too thick. Add salt and pepper to taste.