Whenever you expect someone to come to the door, have her already on a leash and tether her at enough of a distance from the door that her arousal level is low. Pay absolutely NO attention to her when she starts barking etc and ask the person ahead of time to do the same. When she is calm, even for a second or two, ask the person to toss a small, yummy treat in front of her. No fussing over her or eye contact. Have the person not face her straight on, but keep her body sideways and don't look at her. Everytime she has a few seconds of quiet/calm, have the guest toss a treat for her. Keep her at this "safe" distance for a while.
Does she ever settle down, once the person has been there for a whille? If so, bring her a little closer....not too close until she is able to be calm at the previous distance.
You can also use a crate instead of tethering her. Teach her to go to her crate when someone knocks on the door. (practice with family members or friends as door knockers) She goes to her "safe" place and is given treats for relative calmness. When things settle down and if she is able to tolerate the person being in your house, let her out for some handouts and attention from the visitor or practice "visitor." Give attention and eye contact ONLY when she is relatively calm.
The being at a distance tied to door knob or something......or being in the crate is NOT a punishment. It is an "out" for her, a way to help her keep distance which should help her relax and not get overly aroused at the initial "intrusion" of this visitor. You're rewarding/reinforcing calm behavior and showing her that visitors are good things, not bad things. The highly agitated behavior will be somewhat prevented by the distance and by the humans NOT reacting to it, which further stirs her up.
This will be a sort of training program which you will need to actively practice every day a couple two-three times and not only on the occasional time when someone actually is visiting. Get help from family members and friends. Try that and see how it goes and let us know. Good luck.