What can dogs not eat on a raw diet?

My mom is under the impression (advised by her raw food seller and multiple pet store workers) that she is not able to feed her dog any cooked food, along side her raw (her dog won’t eat some things raw, but will eat them cooked). They say this is because their digestive system digests cooked vs uncooked differently and will get ill trying to digest both at once. Everything I have found after quick research says it is fine to feed them raw and cooked, can anyone confirm this?