A post on the Alabama board suggested that the accident took place a year later and involved troops from the 57th Alabama from Pollard. After a dilligent review of period newspapers and service files, I find no evidence of that.
The post mentioned Confederate medical battalions being shipped from Vicksburg to Mobile via New Orleans and other events which couldn't be credited. On the other hand, the source cited for this, an ADAH file on wartime Greenville, does exists. I made a trip to Montgomery just to see it. After a review of several hours, I found nothing in the file to support a second accident.
Ina Mae Porter was a Greenville resident throughout the war. Her account mentions only one rail accident in the area, and I see no reason to discredit it.
If you have evidence of another wreck near Greenville AL, I would like to have a look at it.