I can't help you out on who may have made the barrel. I can help you out a little on the meaning of "single cut". What is meant by that is that each groove is cut individually. The cutter is advanced through the barrel and then it is indexed to make a cut in the next groove. After a pass has been made through each groove, the cutter depth is advanced and the process started again. Many refer to this as being "cut rifled". It is much the same process they have used when they hand cut the rifling in muzzle loader barrels by hand. 
I think that a while back there had been posts on rifleing a barrel and there were several links to manufacturers that showed how they do it.
Hope this helps.
Sam

double set triggers on a Ruger #1 are FAR from standard  I've seen a very few,  most are made by taking out most of the Ruger trigger mechanism and building tuning for a much lighter sear.  then somehow or other fitting a set of DST, possible a Mauser "small" replacement set or I have seen a few that had muzzle loader DSTs shoehorned in.  In some cases the trigger guard had to be enlarged and the lever catch re engineered.  converting a Ruger #3 to a DST is a fair amount easier since you don;t have to work around the trigger guard/lever setup.     It sounds like she has a really special rifle there .   Keep us posted.  Id be interested in seeing some photos of it too.

Wayne Schwartz was well known for installing double sets in the Schuetzen Rugers for both the #1's and 3's in those rifles he built and I have seen a few for sale over the years. If memory serves me right I believe he disscussed it in the Modern Schuetzen Rifle by Charlie Dell & Wayne Schwartz.

JLouis

Didn't Ron Snover cut odd numbered grooves when he was in Penn?