1. I think Shana used the U-turn right, this is a typical situation where you had to use it. Though Lorena/Jason were so far behind, they might not know how far they had to go next and what the next task was, so it could give them more time buffer. And Lorena/Jason did got eliminated, so there was no drawback on them. The only uncertainty was that if this was a NEL, then it would definitely hurt them in future legs.
2. If they were the 7th team at that point, it would never hurt them because no one would know they have used the U-turn, but now TK/Rachel knew that, that means other teams would know it at the pit stop, so this would make Shana/Jennifer less trustworthy to the other teams.