How can I help my 11-month old dog, stop being so mean whenever company is around?

She sounds very aggressive, i think you may need a trainer. for now make her leave before you let company in. Don't let her play the tough guy with your guests. My opinion is that a dog that bites has lost its privilege to be part of the family. Please consult a trainer before she goes any further. Right now she thinks that she is top dog in the pack, and she needs to know that the people in the house are the pack leaders.