Barking???

We have two Shelties Kasey and Lacy. Before my other dog cody dies kasey lived in the pen with him. sense we live on a mountain we dont get much company.So when some one came up they would bark. Well when cody died we moved up with lacy. We dont mide them barking if its a stranger but when were about to leave or we just pulled in the drve way and get out she still barks, when she knows it us! Do you think she doesnt like to be left alone ?