The Winchester '97 was pretty well-known for beating the tar out of the shooter, at least with any load of reasonable power. The Norinco copy is the same.
Adding length in the form of padding won't help much, whether it's on the gun or under her shirt. The overly long length of pull (LOP) is preventing her from using the form she needs to absorb the recoil properly, since she has to extend her strong arm to reach the trigger.
Take the thing to a 'smith and have him whack the stock down, as was suggested, and maybe add a recoil pad (if legal in SASS). This way she will be able to use the correct form and shoot not only more comfortably, but also faster and more accurately.
A side benefit of the correct LOP will be that the gun will mount much faster, which will presumably be an aid in a speed-oriented sport like SASS. The mount will also be more consistent. I am 5'8" and prefer an LOP of about 13" on most long guns, which is about 1" to 1.5" shorter than most factory dimensions. It just works better.
Don't be afraid to cut the stock; it's only a Norinco, with no collector value. She will be much happier with the result.