Employees have no duty to cooperate with a nurse case manager sent by the insurance company. Freeman v ASRC, AWCB Decision No 15-0073 (6/26/15). 
Think of the nurse case manager as an insurance adjuster with a nursing degree because that is what she is. Her job is to minimize the medical benefits paid for an injured worker. She looks for evidence that the injury may not be work-related in an effort to defeat medical benefits.
And, sadly enough, there is one case documented (and probably more which have not shown up) where the nurse case manager directed the injured worker from one physician to another with whom she had an established professional relationship - a relationship so cozy that the doctor signed letters that had been written by the nurse as if he had written them himself. The evidence in the case tends to show that real reason the nurse sent the employee to that doctor was not because she was trying to secure good medical treatment from him but because she was hoping her favorite doctor would say the surgery wasn't needed or that it wasn't work related.
Under the Freeman case, the nurse case manager has a legal duty to inform the injured worker of her role, of the adversarial nature of workers compensation (i.e. she is working against him), his right to decline her assistance and the possibility and likelihood that the insurance company's and the worker's interest may someday diverge.
If the nurse case manager you're working with hasn't disclosed all of her role etc, you got to wonder what's going on.
Keenan Powell has practiced Workers Compensation law in the State of Alaska for over 30 years and has dedicated her practice to Workers Compensation representing injured Alaskans handling hundreds of cases. A sample of verdicts she has obtained for Employees is found at http://www.keenanpowell.com/past-verdicts-settlements.
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