Sounds like she is trying to be protective of you, so you need to convince her you don't need her to protect you unless you ask her to. Try to introduce her to visitors such as the postman and paper boy who come regularly, on a lead and under control. Get them to give her a titbit and praise her gently if she allows them to. If you can, try to separate her from where they post the letters/papers, by putting a postbox outside the house away from the door. Do the same with neighbours, and if they have a dog, try to walk her on a lead with them and their dog. You can also use a water spray bottle if she barks when visitors come, and praise/reward her if she stops barking. It is a case of re-educating her and making sure you let her know that you are not happy with her behaviour.