While your idea sounds well founded, you must also factor in the intangible things, and some of those are the physical abilities of the bowler thrmselves.
If she is right-handed, and you've moved her to the left side of the lane, you have effectively changed the way she sees the lane and slide area coming at her during her approach, and it sounds like that is hurting her more than the ball motion is helping.
Not everyone is supposed to be professional caliber, advanced level, or heck even very good at the game. Some people are just supposed to be what they are and enjoy it for the fun and social aspects of it.
It sounds like she has come to grips with her limitations, and is good with that. If you want her to enjoy the game, let her do it her way, then be the best at that as she can be.