Combine chicken broth and 1/2 cup milk into saucepan and heat over medium heat. In separate bowl whisk 1 cup milk with flour. When broth and milk start to boil, reduce heat, and slowly stir in milk and flour. When fully incorporated set aside to cool. Spray inside of crockpot with cooking spray. Add rice and seasonings to crockpot. Chop up onion and add it with mushrooms. Stir in broth, flour, and milk mixture. Rice may turn red from paprika. Lay chicken on top. Cover and cook on high 4 hours or low for about 8. Make sure to stir before eating!