This is such a sad story, and I hope you have luck in finding information about Sara's father.Since you don't really know where George went, it will be difficult to find his death certificate.It may be easier to locate other people that he may have kept in touch with, and whose descendants might still know about it.
I went searching in censuses and found a little information.
George was living with his family in 1930:
Tallassee, Elmore County, AL.ED 4, PAge 2B.
Dwelling 38/Family 39.Farm (rents)
George W Lindsey, head, white, 51, married, age 18 at first marriage, reads, writes, he and parents b LA, Farmer
Carrie M Lindsey, wife, white, 43, married, age 40 at first marriage, reads, writes, she and parents b Alabama
Sarah E. Lindsey, daughter, white, 1 year, 1 months, b Alabama
Judging from this entry, it looks like George and Carrie were married in 1926 or 1927, and that George was married before (just before the turn of the century).It would be interesting to discover whether he had children from that marriage whom he may have kept in touch with.
Since you have an idea of where George was born (Claiborne Parish), I checked the 1880 census for that parish, hoping to find the names of his siblings.Surprising, I didn't find a George or G.W. Lindsey/Lindsay anywhere in Louisiana who was under 15.There was only one family named Lindsey with small children in Claiborne Parish.It is possible that George's birthday was slightly off, and he was born after the census, (or this might not be his family at all).
1880 LA, Claiborne Parish, LA
ED 9, Page 28D. Dwelling 259/Family 269.
William B. Lindsey, white, 45, farmer, b Al, parents b SC
Malinda, 30, wife, b Al, father b AL, mother b GA
Sarah H, 8, daughter, b Arkansas
William, 7, son,b Arkansas
Mary A, 6, daughter,b Arkansas
Lezani L., 5, daughter,b Arkansas
Samuel W., 4, son,b Arkansas
Mildrid T., 3, daughter,b Arkansas
The LA death index lists an entry who may be the Mary A. listed here:Mary A Lindsey, age 72, white, d 8 Aug 1947 in Claiborne Parish, LA.Vol 9, Certificate 772
Unfortunately, I don't have access to a census index for the 1900 or 1910 census, so I can't follow this family through the census to see if young George was living with them, or to find out what happened to the children.You may want to contact the Claiborne Parish Courthouse to see if they have a probate record for William B. or Malinda Lindsey.Those would likely list all of their children, thus letting you know if George was a member of this household.(The courthouse may also have a record of George's first marriage.)
Also, was there a postmark or a date on the letter that George had sent?That may give you a starting place to search.
You may also want to post your message on the Claiborne Parish, LA and Elmore County, AL genweb sites, as well as on the Alabama genforum forum, if you haven't already.
I'm sorry I can't help more, but best of luck to you!!