Place the chicken breast in the slow cooker.
Chop the carrots, celery, and onion, then add them to the slow cooker. Sprinkle thyme, rosemary, salt, and pepper over the veggies.
Add the chicken broth. Set the slow cooker to high and let it cook for 4-5 hours or until the chicken is fully cooked and easily shreds.
Once the chicken is cooked, remove it from the slow cooker and shred it using two forks. Add the shredded chicken back into the slow cooker.
Stir in the egg noodles, ensuring they are fully submerged in the broth. Continue cooking on high for an additional 10-15 minutes or until the egg noodles are al dente. Be cautious not to overcook the noodles, as they will continue to cook slightly even after turning off the heat.
Ladle the soup into bowls and serve. I like to strain the broth out for my kids as it is hard for them to use spoons. This makes it easier for them to eat.