Following an upset in her bedroom, an older daughter storms into the kitchen saying, “I hate her! She is always ruining my stuff!” Unfortunately, common parent responses include giving logic or reason, “she is younger than you, you have to be patient,” or a demand, “she is your sister, she is going to be your best friend in life,” or, “we are a family of love.” Worse yet, parents might deny the emotion overall, “you don’t hate her, you love her.” All of these responses teach the older child to bottle emotions, teach that her emotions are wrong and give her something to argue about. These responses let her know that you don’t understand.
it’s better in these moments to understand her emotion, give empathy and validate her emotion. This would sound like, “wow, you are mad at her! You don’t want her in your room.” The parent is labeling the emotion and letting the child know she is understood, that her emotions are her own and they are important. The child feels connected and can safely express herself. She can move forward from the emotion, rather than have to hang on to it and argue.
I am not saying you have to allow the word “hate” or let them scream negative things at each other day in and day out. You can follow-up by curbing the words as you would behavior. After you’ve given empathy, and the situation has calmed, it’s fair game to loop back by saying, “I know you are mad. When you are mad, I need you to find a better way to say it.” Then talk with your child about better ways. You might curb the language moving forward with, “those words are too hurtful. If I hear that again you will be in separate rooms.” Also, it’s good to spend time with both children addressing the specific behaviors at hand. This may be coming up with house rules about being in each other’s rooms, or setting aside time when they play separately each day to give them a bit more elbow room.
If you want to learn more about sibling relationships, there is a great book titled Siblings Without Rivalry by Faber and Mazlish.
Parenting by Dr. Rene 
Do you have any advice for a 7 year old brother who, at times, needs to show more patience toward his younger brother (4.5 yrs)? He is not telling his younger brother that he hates him or anything extreme but he can snap at his brother who is not doing anything necessarily to provoke him. Thanks!
There is a good children’s book that introcudes the idea of patience titled Remy the Rhino Learns Patience. There is another book that highlights a younger sibling copies an older out of love titled Do Like Kyla.
You might talk to him occasionally, when all is well, about how much his younger brother loves him and how it must feel to be snapped at. Do this in a real calm, low key way. To best sink in it shouldn’t feel like a discipline conversation at all.
In the moment, you might give brief empathy and have him find a better way to say, “I can hear you are upset, find a nicer way to say that please.” If he is unable, give him a bit of time or brainstorm a few examples.