How can I help my kid overcome her shyness?

As a formerly shy kid myself, I think it's best for you not to force her to come out of her shell, but give her plenty of opportunities to do so. Encourage her when you see her being more outgoing, but don't make her feel bad for being shy. In fact, I wouldn't draw her attention to her shyness at all. What's important is that you build up her confidence. :)

You expose your kid gradually to close friends and other family members first, then to other people, then eventually to a larger crowd. Help your child build her self-esteem as well so she's confident to mingle with other people.