Am I forgetting things? Before this scene, Hook was the only person who knew that David’s father died by sword rather than by drunken accident, and Emma never knew what her grandfather looked like. She immediately assumed the worst possible interpretation of what she saw in the dreamcatcher. Her guess turned out to be true, but it wasn’t based on adequate evidence. If Emma is willing to leap to that kind of conclusion about Hook in the absence of evidence, then regardless of whether he’s ready to marry her, she’s not ready to marry him.