She could probably do a 14lb spring. Yes, she has issues with racking the factory spring. The gun she has now is the 5" Tactile. The Springfield Armory pre cut optic slide conversion kit (slide, barrel, and spring) converts it from 5" to a 4".
My Mom has the XD9 Tactical 5" with a 13lb recoil spring. I recently purchased the Springfield precut optic slide conversion kit. The recoil spring that came with the kit is 18lb captured recoil spring. I have looked all over, even the same site where I purchased the 13lb uncaptured spring for...