You don't cure shy. You can't.
Only thing you can do is offer support and give them the freedom to explore with the safety that good support can bring.
She's not going to have trouble making friends. She'll be selective about who she considers a friend. That's not a bad thing. We all have to surround ourselves with people that match us and/or balance us.
That balance is what you encourage. Finding her own path to friends she, she feels connected to and safe with. Once she finds them in her own way, in her own time, you provide the opportunities for them to spend time together so that those friendships grow and develop.
Being slow to warm up, being shy, it's not a bad thing. It's just one way of experiencing life.