I asked Professor Higgins about this, and he said he has never oiled a holster in his life. So I set about loosening it myself, and it took less time than I expected. The holster was made to fit the gun, but it took some force to get the gun to go all the way into the holster. Shoving it ALL THE WAY IN is good policy, as you surely know.
Then just leave it there. She won't mind. Then I had to sort of soften the upper edge of the holster so it would be easier to get the cylinder past the upper lip. As i say, it did not take as much work as I expected.