Pre-teen root issues causing behaviors

I feel that in our home we are doing well with the four skills when it is obvious things; however, I find it more challenging when the root of the behavior is not as obvious. For example, this past week our oldest daughter (who is almost 12) has been very grumpy and rude to everyone in the family. She has accepted her consequences, but she was still not changing her attitude. My husband asked me if it was because we had to reschedule a shopping trip I was going to take with her. I pulled her aside and found out that this was part of the reason, so we were able to discuss why we had to change our schedule and when we would do the trip. She also confided that she was not happy with the budget for the trip, as her friends get a larger budget for back-to-school shopping. This gave us opportunity to discuss some heart issues she is having. So my question is what advice can you share with parents entering the pre-teen world on how to identify these root causes for poor behavior and would doing the course "The value and Mastery of Emotion" be a good resource to do with her? We have the TSG on-line course.