It does not sound good, but with out knowing more about your set up it is hard to know what the problem is. Assuming that your temps, substrate and other enviromental factors are ok, it sounds as if the snake has gang green in her digestive track, possibly from food rotting in her belly (normally a sign of too low of temps. If the area is already hard, lumped and discolored, it may already be too late to save the snake without extensive Vet intervention and possible surgery to remove to dying tissue. I know that this sounds horrible but your brief description sounds as if this is the case. The food would have caused an obstruction in the intestines, making for the lump and the runny discolored stool. the discolored area around the lump is the dying tissue inside the snake. I wish you luck but I do not think it is good for the aniaml in any way. Others may be able to provide a more hopeful opinion, but this is what I believe it to be.
Sorry
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Jim Hopkins "Hoppy"
Hopkins Holesale Herps
Hopfam1@aol.com