well ruger lists the entire line of sp101 as a snubnose revolver. and you can get 3.1 to 4.1 inch barrels now. Not the greatest of help but its not meant to be.
To me, a "snubbie" has a barrel just long enough to get the bullet going in the desired direction. That's it. Close-quarters work only, not much thought for accuracy past 10-15 feet. Others will correct me, but I don't know that I've seen a revolver with under a 3" barrel with anything more than a groove for a rear sight - another qualifier of snubbie status in my book.
Aw crap, I just checked my 3" GP 100 and it's got a groove rear sight. OK, ok, so a snubbie is a SMALL-framed revolver with less than a 3" barrel AND a groove rear sight. Right?
I think you need to remeasure the barrel on that Colt Pocket Positive, it almost for certain looks to be more than 3" (measure from the muzzle back to the front of the cylinder).
Here's a picture of one with a 2-1/2" barrel. Quite a difference between that one and your wife's.
I, myself call a "snub revolver" any small or medium frame wheel gun with a barrel 3" or less.
L or N frames or the big Ruger AK line(based on the Super RedHawk) could be snubs too.
I used a snub Taurus Ti Protector .357magnum on a security detail in 2004. FWIW, the security supervisor wouldn't let me use the firm's brand new 686 4" L frame, & the gun shops in the area(NW Florida) had a limited selection.
I purchased a larger Ruger GPNY wheel gun to use a few years later. A few of the local sheriff deputies gave me a hard time about using a revolver so I was tempted to buy a NIB Ruger GP100 .357magnum 6" barrel just to be a jerk!