Thank you. There may just be an adjustment period needed or Sadie could be worried she will get hurt or Sadie is possessive over things in the home. It is difficult to say with so little information what exactly the problem is. What I would try is first to put all toys, bones, & food bowls away to make sure it is not possession. Then I would leash the new dog let your friend hold the leash and allow the dog to be in the same room with Sadie, but at the same time you will reward Sadie with a high value treat. such as hot dog or chicken when she behaves no growling or snarling. But you must show her that you have the other dog under control or else she will continue. We call this behavior adjustment training. The premise is to have Sadie understand that when she reacts appropriately something good happens as well this only happens when this new dog is near thereby eventually having Sadie not mind the new dog being near her. You will have to watch Sadie's level of distress when you bring the other dog around her and know when to move the new dog back a bit. Everything has to be done in small increments until you get to the day the two dogs can be together in one room without problems. IF you rush it then you will have the same problem and it may create more stress on the part of both dogs which can lead to more dislike between them.
I would definitely get a command such as leave it on both dogs so you can stop Sadie's actions with a command. I would use clicker training as it is positive reinforcement training. If you are not sure how to teach that I will direct you to a site that will take you step by step in basic obedience.
I will also direct you to a site for BAT training which has videos and will give you an idea on how to train a dog gradually and using reward.
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Here are sites for clicker training that will show you how this is used.