My cousin has pain in her right hand in the elbow region. when we consulted a doctor he said, it is because of lymph nodes in the neck region.?

Elbow pain: May come from a multitude of causes: nerve, vessel, ligament, muscle, tendon, joint, lymphatic, etc.

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells/digested food. Lymph nodes "taste" the lymph everywhere for bad stuff like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.