This website Norway-Heritage "Hands Across the Sea" is visited by volunteer researchers who have expert skills in Norwegian genealogy. They will answer right away if you post a query, probably, and they may have questions, so be standing by at the ready to respond if so. Be sure not to walk away from the forum to let them "talk amongst themselves." http://www.norwayheritage.com/http://www.norwayheritage.com/
They will want Susan's immigration year or approx (1900 census), birth month and year (1900 census) or birth day/month/year even better. The names of her children can be a clue to the names of her parents. Note her location in each census year for them (she could be moving to join a relative, etc., so location can be a clue). If you have her full name, great, say it. If your friend has a marriage record, or death certificate, or birth certificate for her children, mine those for every detail you can get from them.
Without any of the key facts, it may be hard or impossible for the forum to help. So I recommend developing as much as possible in the USA first. Find an obit for Susan, write to the (Lutheran) church in her South Dakota community for records, etc.
I guess that's like diving into the depths of information about her, rather than swinging your net wide and shallow.
In Norway she will be Susanna or Synneva etc. Pedersdatter/Pederson and also as you probably already know she'll have a place name on the end.
There are "lags" in the USA whose members are of Norwegian heritage but it's hard for you to work with them because you don't know what part of Norway Susan was from, and these groups focus on a particular region.
I highly recommend this fabulous (and free) Norway-History forum. Hope you find your friend's Norwegian roots.