It depends on the child. Some will have no problem going along with you. In that case, I would make sure basic needs are met. Food, water, warmth, finding a safe place, and locating the girl’s guardians would be my priorities. I would also try to find something she can use to stay busy and calm herself. A soft blanket or toy, maybe. If she likes her grandpa, I might take something that carries his smell for her to keep. Drawing can also help children deal with their emotions. In a pinch, even something like a cool rock for good luck can help a lot. If you have a handkerchief, turn it into a tiny, friendly ghost – kids need something to literally hold on to in difficult times.
If she’s very shy or distrustful, I would try to give her space. Not too many questions, and no pressure. Shy children generally don’t like being watched, so I would try to keep myself busy. Even though I would probably want to comfort her, I think that can backfire when kids are just not sure whether you can be trusted. Sometimes, (shy) children have a special interest or maybe a companion that is a path to their trust. If the kid is holding a doll, I would try to ask questions about that. “What’s her name? How is she?” When you need children to cooperate, accepting their magical world of imagination is one way to earn trust. It’s also a good way to learn about a child’s inner state, as they very often share a soul with their special stuffed animal or imaginary friend.
All children I have ever met have been grateful and even relieved when there was room for their emotions. So I try to notice feelings instead of saying things like “Don’t cry” or reacting with impatience to their frustration and anger. I simply say “You look angry. Why is that?”
My youngest sister is only three, and she is a somewhat reserved child. When she feels emotions she cannot handle yet, it really helps her when I talk about that instead of trying to jolly her out of it. Just last week, we talked about homesickness. She becomes visibly happier and more open when she realises her emotions are normal and that the adults in her life get it.