You asked

How do I stop my little girl from pulling her hair out?

Trichotillomania is a disorder that causes people to pull their hair out form their head, arms, legs, eyelashes or any other part of their body.
Like most disorders, it varies from child to child and while some can quell it with concentration and determination, this can be hard for kids who become overwhelmed by the urge.
It is important that you keep an eye on your daughter to try to determine if there are certain triggers that set her off. This way you will be in a better position to help her out.
Fortunately, this behaviour may right itself without you having to do anything; however, if your little one is pulling out so much hair that they are suffering from a bald patch it would be a good idea to take them to their GP.
Stress, frustration, anxiety and social issues can exacerbate the problem and it may very well become a lifelong struggle that your little one has to deal with.
The younger your little one is when you tackle the problem the easier it will be so try to direct her behaviour away from the pulling. Get them to wear a pair of gloves or tie their hair up tight so they can’t pull it. If it is just the hair texture that she likes, get her to hold a stuffed toy or give her a hairbrush with hair in it.
It is vital that you avoid any form of negative behaviour when addressing the issue. Never shout or pull her hand away and avoid using the word “no”. Your little may use it to comfort herself and by getting mad you will just exacerbate the problem.
It may be just a phase that your little one is going through; however, while it may disappear in a while it can reappear again in times of stress. 

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