naughty dogs

getting really frustrated by the behaviour of our oldest dog.  She has turned quite nasty towards our middle dog, attacking him when hubby comes home.  She has done this before and it stopped but the last couple of days she has had him and positively tried to kill.  I would blame the introduction of the puppy but he has been living here for 7 weeks now.  Hope it all sorts itself out soon as the middle dog is looking nearly as depressed as me. :(