Next time when your friend call you to pay $300, how about telling her to bring this case to small claim(court)? The process may take long time, but the Judge will decide what you and your friend should do! There is no proof your kid broke the guitar, and your friend will not bring the case to the court. If she bring the case, I don’t think she will win! The accident was happened almost 3 months ago, and she is the one who said ”Don’t Worry about the guitar!!” to you.