I know this is an old thread, but I did some research into the tribes in Idaho, and makkarana is flat out wrong. First of all, skin walkers are a myth that is completely contained to tribes of the southwest, and the only kind of tribe that I even found that was mentioned to have any relation to the skin walker at all was the Navajo.

Second, there was an AMA done on askreddit a few months back where a boy from the Navajo Nation answered questions. When asked about the skin walkers he stated very clearly that they are most like sociopaths, not cryptozoology. This also plays into what makkarana said about skin walkers. Most sociopaths are also male, and it is rare to find a female sociopath.

Third, people like to lump all native americans into one group. They are not. Each tribe has there own lore, myths, creation stories, languages, customs... etc. It is really fucked up to try to group them together like that. For the area that this story occurred in, the local tribe would be the Nez Perce. They do not have the myth of "skin walkers." I was unable to find much information on myths they do have about shape shifters, but from what I did read it seems that either these people are a type of animal and stay that way for the most part (Nez Perce myths talk about several men being involved with bear-girls) but in general, shape shifters are considered evil by almost all tribes.

The myths I found that did mention women shape shifters say that they are usually women who try to lure men away into the forest to kill them for sins they have committed (excess drinking, adultery, gambling, etc). They are considered dangerous by many tribes, although not all of them consider them to be evil.

You should be able to find all this information by searching for "Nez Perce myths" and "native american skin walkers." Sorry for the long comment on such an old post, but a lot of people seem to be blowing up this whole skin walker thing (probably because of /r/nosleep) and I read through that AMA as well as Navajo mythology and information posted about skin walkers by other Navajos and I just want to do my part to keep from ignorance being spread is all.