Whether she's your girlfriend or your sister, you will need to be tactful and patient when trying to calm down an angry girl. A few poorly chosen words or gestures and you could wind up worsening her mood -- even when you have the best intentions. In some cases, you might even lose your own temper, leaving you both in negative moods. Rather than risk straining your relationship, learn a few strategies to help cool her mood and address what's really bothering her.

Have the Right Attitude

Set your own emotions aside when dealing with an angry girl, suggests the University of California, San Francisco article, "Chapter 15: Conflict Resolution." In her temperamental state, she might seem to take her anger out on you, casting glares, throwing insults or simply giving you the cold shoulder. Don't take any of this personally. Take responsibility for being the source of calm in this encounter, and don't let her bad mood contaminate your own peace. Remember to breathe slowly and deeply to keep your own temper under wraps.

Lend an Ear

Angry people are in need of an imaginary cupcake, suggests licensed clinical psychologist Nadia Persun in the PsychCental.com article "How to Switch Off an Angry Person." By this, she means that this angry girl feels like someone -- or perhaps even fate -- has wronged her, and you can ease her sense of helplessness by taking her side. While you don't necessarily have to agree with her, or even offer her advice, show an interest in her problems. Ask questions and restate or rephrase her answers to show you are listening.

Reserve Arguments

A angry person -- male or female -- will have a hard time understanding your attempts at logical reasoning, suggests licensed psychologist Lynne Namka in the "Angries Out" article "So You Love an Angry Person." This is because she's being flooded with hormones that impair clear thinking. If you have an argument or counterpoint to make, reserve it until she seems calmer. Otherwise, you risk further stirring her anger, or making her feel misunderstood.

Problem Solve Together

If you see a way you can help her solve her problem, offer to help, suggests psychologist Irene S. Levine in the Psychology Today article, "Guest Post: 7 Ways to Cheer Up a Girlfriend." For example, if she's upset with herself over a bad grade, offer to tutor her or help her find some classroom assistance. If there's little you can do, or the problem is something that she will simply have to accept over time, you can continue allowing her to vent or treat her to something that will distract her from her anger. For example, go for a walk together or watch her favorite movie.