How long do you continue to try to help a person?

Sometimes all people need is time. The girl you talked about is surely upset and I think she needs to stay a little by herself to think. That doesn't mean you have to stop caring about her: make her feel loved, let her know you will always be there for her, but don't overdo it. Remember: her problems are not YOUR problems. All you can do is being there, but she has to find the strength to change all by herself. Good Luck!