It makes perfect sense to me.  Did you miss the part about "the history of the walnut production died with her brother and his widow is MIA"?  Mom leaves the  orchard to Sis because neither of them like Bro's wife and the worthless stepchildren.  But Sis doesn't want to kick Bro off the property, he's the one who knows how to manage it, so she tells him "you can live there the rest of your life, but when you're gone so is Floozy.  I get the property back for myself, to keep in the family."  Because that's probably what Mom told her to do.  

So I'm not sure why there would be a step-up in basis.  She's owned the property since 2013.  If she had given the brother a 10-year lease on it, her basis would have remained the same.  Except who was entitled to depreciate those trees?  Too early in tax season to consider such squirrelly questions.