My guess would be a "limp wrist" issue. I hate to blame it on this because there are some other polymer framed pistol companies that blame the shooter instead of the gun but in this case we should at least take a look at it.
How is her grip? Mrs. Dodge had short stroking issues with her EMP so we changed her grip so that her left wrist (she is right-handed) pivoted forward and locked and the issue has disappeared. This link may give you a better idea on how to improve things: LINK
I am sure that the pistol is also a little tight right now. Get another couple hundred rounds through it to let everything settle in and the recoil spring a little softer. If it still doesn't run right, I would check with S&W's excellent customer service department to see if they have any suggestions.