Any parent can tell you that having a child is an amazing adventure. Through the years with your child, you will experience many ups and downs as part of the job. It would be great if all children hit adulthood and were perfect, model citizens. Unfortunately, parents and children are human and everyone makes mistakes. Dealing with a disrespectful adult child can be one of the most stressful issues that you will have to experience. There are some things you can do to alleviate or rectify the issue.
State your feelings. If your child is being openly disrespectful, in a calm voice, point it out. Say something along the lines of "I really don't appreciate the way you are treating me. I would really like it if you stopped." You can also say something along the lines of "I will not take this kind of behaviour."
Realise that you don't need to take the disrespect. If she is treating you badly and won't stop after you ask her to, you can walk away or tell her to leave your home. This might hurt, but sometimes the best thing to do is to postpone the conversation until both parties are calm, collected and have had time to think about the situation.
Ask your daughter what is bothering her, and be open to listen and communicate with her. This will open the door to a discussion about the situation and feelings. Be willing to hear things you will not like. Sometimes honesty can really hurt, but it is important to discuss this problem. This experience can be very humbling if you hear truths about yourself that you didn't realise. Getting it out in the open is better than pretending there isn't a problem.
Write your feelings on paper. This is a good outlet for residual feelings you are having. You might be surprised by what comes out. After writing everything, burn the paper. It will help to let it out and express your anger, pain and sadness without escalating the issue and hurting feelings.
Look at things from your daughter's point of view. Many people project their feelings, judgments and insecurities onto others. Even though she is directing her anger and frustration at you, it could be an indicator of how she is feeling inside. Look at what behaviours she is expressing. The "louder" an emotion or feeling is, the more it needs to be addressed. For example, if she is calling you mean, maybe she is not recognising and dealing with her own anger issues. If she is calling you nasty names, she might be denying that aspect within herself.
Remember that life is about learning. Although your daughter is an adult, she is still learning about life, as is everyone else. If you think about it, you are still learning about life as well. This experience with your daughter is a very important learning lesson. Maybe by showing her that its not all right to treat people like that and expressing your feelings, she will realise that parents have feelings too and they deserve respect like everyone else. It will also help you to grow as you learn to communicate, stick up for yourself or when to walk away.
Model the behaviour that you want your daughter to learn. Even if you want to scream, insult or be mean back, stay calm and express love throughout. Work through the issue this way. Preventing the issue from escalating and demonstrating that you can show love regardless is important for your daughter to see.
Don't be afraid to tell your daughter to leave your home. This might be very difficult, especially if she is living with you, but sometimes tough love is the most powerful lesson. Once she is gone, she could come to realise that she didn't have it so bad after all.