To exclude the income under §112, the compensation received must be for active service in the combat zone as a member of the United State Armed Forces.

§1.112-1(a)(4) goes on to stipulate compensation paid to your client as a civilian is not be eligible for the exclusion:

Compensation paid to civilian employees of the federal government, including civilian employees of the Armed Forces, cannot be excluded under section 112, except as provided in section 112(d)(2) (which extends the exclusion to compensation of civilian employees of the federal government in missing status due to the Vietnam conflict).