We have a Catalan Sheepdog (Fizz). She has only been here 5 days, but now that she is settled in, she's starting to play-bite, bark at and jump up at my sister (but no-one else). My sister is quite scared because she is normally very, very calm and sweet-natured, but she can get over excited by her dressing-gown, start pulling at it and get worse from there! Can anyone help?!