It may seem like locking her in another room is just avoiding training her...avoiding the stimulus which is getting her into an almost panicked or manic state. However, she can NOT listen or focus on you AT ALL in such a state. There is NO reaching her or connecting with her when her fight or flight is so high. So, I recommend practicing with a family member or friend and have them come knock on the door and meanwhile you have her on the leash and take her to a crate or another room some distance from the door...calmly and take with you a Kong toy stuffed with peanut butter or chicken, something good. Put her there and use a cue word every time like, "go to your room." Or something shorter...."room" "crate." Practice this several times a day spread out over the day. Then go open the door and have the person sit down and chat. When things are calm, let her out....not if she's raising a fuss, but when she's quiet, even for a few seconds.
Normally, it's the initial arrival of someone who triggers this crazed state and the door knocking is the predictor of this upsetting event. So, what you're doing is making the door knocking sound be the predictor of a calming event, going into a safe room with a high value treat/toy. You're diffusing the anxiety.
When you've practiced this for quite some time, you will be able to use your cue word to send her to her room or crate....her comforting place when there is a knock on the door. Eventually, you won't have to lock her in, she'll just be conditioned to go to her safe place when she's panicked like that. This response that she has when someone comes to the door very most likely is derived from fear. It sounds like a defense "aggression" type thing. Or just flat out alarm.
She will probably still bark when she's in the crate or room for a few minutes. Wait until things seem more normal and steady to her....wait for her to quiet and then bring her out. Don't pay any attention to her while she's barking or whining. Wait for good behavior to give her attention....you and whoever is visiting. You'll definitely need someone to be your door knocker.