Here it is:  the fix for shoulder blade/scapular weakness on one side that makes progressing your P90X workout, or any upper body workout for that matter, harder.  

If you follow the above  links you will see how to strengthening one-sided shoulder girdle problems.  When the shoulder girdle is weak, it can cause winging.  If it is just a little weak, like it is with this lady, then you may have headaches, because of the stretch to the upper trapezius.  You might also develop rotator cuff impingement due to this problem.  

How do you develop shoulder blade weakness?  Usually it hppens because you might have an arm injury, which can make your muscle weak as they try to protect you and stop you from using an injured body part.  Other causes can be prolonged computer use in which your arms and shoulder are held in the shoulder forward position.  

Good luck