My girlfriend has chronic neck pain and cracks her own neck. it makes a very loud pop, and sometimes causes "shocks" down her arms. is what she is doing safe? if not, what problems could arise?

Possible arthritis: Popping neck may be ok since many do it without ill effects. But, "a shock down arms" means that the pop irritates her nerves going to the arm. Look up "brachial plexus" on the web. I worry disc injury or herniation. It is unclear if she has arthritis. I would keep back and neck straight and supported most of time. Avoid awkward position reading or watching tv. Would quit popping. See doc for xray.

Nerve damage: The popping should give relief. If it is making pain or shocks down her arms then the motion is most likely touching a nerve when she does it. As long as the symptoms are transient, then no damage is being done.