Kind words appreciated! Your sister's K-38 won't be hurt at all by reasonable amounts of .38 Special +P. It takes HUGE round counts of this stuff to kill a K-frame.
However, you and she should be advised that a factory-produced 5" K-38 is a rara avis
. They were produced in small quantities, for departments including the Illinois State Police. It would be worth sending a letter to Roy Jinks to determine its origin and track its provenance, but if it's a factory 5" Model 14 it's definitely a collector's item and worth a premium. You or she might also want to register at www.smith-wessonforum.com
, and open a thread. There is a tremendous brain trust of knowledgeable S&W collectors and historians over there, who could offer some history on these special-order guns, and a good idea of their value in the current collectors' market. Include a photo, or at least let them know whether it has a ramp or a Patridge front sight.