I have not been able to verify if Sallie was the widow of your Thomas Dunn

Thomas Dunn, Private, Company D, 3rd Regiment Tennessee Vols. (Lillard’s), enlisted May 6, 1861 at Benton, Tenn. for 12 months, detailed as Teamster April 11 to May 8, 1862, wounded August 6, 1862[?], last recorded at the June 30, 1864 muster roll, dated September 30, 1864 as absent without leave since September 2, 1863, no further records

Note, there are no further Company D muster rolls in the records, hence, we are not aware of subsequent service which would appear to be negative

M268x: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Tennessee

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Sallie, Dunn, widow of Thomas Dunn, Polk County, filed for Confederate Widow’s pension W3042
Source Information
Ancestry.com. Tennessee, Civil War Confederate Pension Applications Index [database on-line]. Provo, UT, USA: Ancestry.com Operations Inc, 2005.

Note, the applicant had to be a resident of Tennessee to apply for and receive a pension from Tennessee.
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Company D, 3rd Tennessee Infantry was raised with men from Polk County.

Benton, Tenn. is in Polk County