I think the key here is that it's an illogical conclusion that is correct.
The stem said that if S did it neither her footprints nor her fingerprints were left at the scene.
Only fingerprints were found. What's the missing part here to make S the guilty party? That they were not her fingerprints. (They could be the victims for all we know).
ALL you had to know was that for S to have done it, neither her footprints nor fingerprints were at the scene.
That's why TCR is that the fingerprints were not hers.
This will, I'm sure, be debated until 12/22 when we find out for sure.