There are a lot of Nepalese students there (Atleast there were quite a few  two years ago). I know for a fact that they have a Nepali Students Club. Dr. Dev Shrestha, a fellow Nepali, is a professor there as well. You might want to contact him/the website for more information. 

In my opinion, Idaho is not the best place to be in, but definitely not the worst. While its pretty aloof from the Northwest culture in Seattle and Portland, Moscow is quiet and relatively cheap. If your sister wants to get her PHD, she'd be fine. Who needs distractions when they are in grad schoo, right :) ?

Hope that helps.