Sometimes it is difficult to separate out psychologic response to pain from the pain itself. A recent study of patients with whiplash associated disorders (WAD) offers some insight into this dilemma.
Patients were given a psychologic exam then treated and tested again. The treatment consisted of cervical (neck) radiofrequency neurotomy (CRFN). Radio waves are used to generate enough heat to cut the nerve that carries pain messages. Patients got pain relief, muscle relaxation, and increased range of motion with CRFN.
Psychologic tests given again after treatment showed that all psychologic distress present before CRFN was completely gone after pain relief from CRFN. This is proof that at least for some patients, the psychologic changes occur as a result of chronic pain not the other way around.
When there's no treatment that can offer pain relief, then behavioral counseling has a role in helping patients learn to cope with their pain. If your sister has already tried various conservative measures, then CRFN may be the next best option before giving up hope for recovery.