Not a picture of your wife's ancestor, but another young man who served in the same regiment and suffered the same fate of capture. Both of them were imprisoned at Andersonville. This guy died there. Forrest Stock was transferred to the Florence Stockade and died shortly after.
View attachment 92457
http://www.fadedfootsteps.com/veter...kin-company-i-8th-michigan-cavalry-union-army
Code No: 68639
Grave No: NOT BURIED AT ANDERSONVILLE
Last Name: STOCK
First Name: FORREST
Rank: PRIVATE
Company: D
Regiment: 8
State: MI
Branch of Service: CAVALRY
Date of Death: 1/24/1865
Cause of Death:
Remarks: Died in prison at Florence, South Carolina.
Reference*: 8TH MI ADG RPT 146
Place Captured: STONEMAN'S RAID TO M (Macon, GA)
Date Captured: 8/4/1864
Alternate Names:
Status: SURVIVED ANDERSONVILLE
More Information Available: NO
Age at Muster 38
This link will take you to info about Florence National Cemetery. Its an interesting read, but will be especially so for your wife, since her ancestor is buried there.
http://www.nps.gov/nr/travel/national_cemeteries/South_Carolina/Florence_National_Cemtery.html