From what I've seen myself, finding a great looking 4 point that will go into the 160 and 170 range won't take too much hard work. But on a unit like the Henry's you need to put in some time and find a 190 class buck, which should be your target for the area. They are there. Any buck under the 180 mark COULD feel disappointing after she's shot him.
However, it's up to your sister-in-law and she can shoot whatever she wants. It's never a guarantee, but I'm sure she will come out with a beautiful buck. We all want to see it when she's done..!