how to know if it is safe to go out with a new-found friend?

It's true that you can't get to know someone unless you spend time with him/her. But then it's not safe to go out with a complete stranger. I think what I'd do is to go out as a group with some of them as your friends. Then you can get to know that person better in a safer setting.

In a way she's right, how would you befriend a stranger if you don't spend time knowing that person? But I don't know what you mean when you say "go out?" You could get to know someone without getting into dangerous situations, like, since she is a woman, she must not be with people she doesnt know especially at night, or alone with the stranger in a car. I think you have a reason to be concerned if this is what she is doing. If I'm interested to get to know somebody who is still a stranger, I would set up meetings with this person in public places, or with a group of friends. It's really common sense. If immediately jump into the vehicle of a man I barely know in the middle of the night after he threw me some pick-up line in a bar, ,just because he looked cute and nice and I want to get to know him, then I'm defintely courting trouble. So go ahead, warn your friend.