It depends on whether or not you can train her to recognize the sound of knocking on your door. Begin by showing her your front door and explaining to her clearly what knocking is. Then, knock on it yourself to show that it’s harmless. Do this a few times until she learns to associate the sound with a human. Once she begins to understand, take her inside and sit her down close to the door. Knock again until you’re certain she still understands that the sound itself is harmless, then close the door and knock once more. Continue knocking it until she understands that knocking is simply a sound made by a friendly human or pokémon. Do this every day until you condition her to stop screaming whenever she hears someone at the door. You can also reinforce this behavior by giving her a treat whenever she’s quiet before you answer the door.
If you can’t train her, then I would recommend earplugs for you and your guest.
The Pokédex According to Bill 