Watch the The Right Elbow online guitar lesson by Bruce Arnold from Guitar Physiology Survival Guide
The only purpose that the elbow has in picking is moving the arm so the pick can access different strings. In reality most of the time you don't even need to move your elbow because your forearm has enough movement to reach every string. This is true whether you are picking or strumming. It should also be pointed out that your inner forearm rests lightly on the guitar. This is another place that students commonly cause stress by pressing their arm into the body of the guitar. Usually you can tell if you are doing this by the change in angle of the guitar and by looking at your inner forearm to see if it's turning red from the pressure. Obviously creating tension anywhere is bad so watch for this problem.