Shauna -- the character we were all supposed to relate to in the past and present timelines for the first couple of years of the series -- is becoming the real villain. She knew Misty didn't tamper with her brakes (just normal wear and tear, as Shauna knew), yet she continued to blame her. She knew Misty didn't lock her in the freezer, but she continued to blame her. She wants to be the victim and blame others.

(My favorite and completely unrelated line in this episode is when Van asks Hannah, "Do Mulder and Scully get together?")

The interesting question at this point is, put yourself in the place of the girls in the past timeline. Some of their actions can be explained (the deaths and cannibalism of Jackie and Javi), just for their survival. But what about Coach Ben? Or the obvious murder of Edwin, the frog researcher? How can they cover that up, or explain it?

Kodiak and Hannah both know Edwin was murdered. For the girls to be rescued and survive without any criminal charges, there can't be any living witnesses. Kodiak and Hannah can't survive the wilderness, and none of the bodies can be found.

Also, why did adult Melissa send the tape to Shauna instead of just burning it or throwing it away? Didn't she realize that would just stir up and create new issues?

I think Shauna's character arc has been absolutely intentional on the part of the creators. In the first season, and into the second, Shauna (teen and adult) was the relatable character. She lost her best friend, she lost her baby, she suffered more than any of the survivors. As viewers, we identified with her more than any other character. And now she's becoming the villain in both timelines. I don't think that makes the show "difficult to watch," but it does make us realize that no one is exactly who they appear to be, and everyone has secrets. And it also makes us question our own beliefs, which adds an interesting level to the series. If someone we thought was heroic becomes a villain, maybe we should question our beliefs about the other characters.