Hey stormdamage,
First question I need to ask is what ball is she currently using with the lefty pin that doesn't get up or slides past the breakpoint? If it is a weak to mild reactive, you may be right in choosing a stronger cover. Second question is what area of the lane is she playing? If she is throwing the ball into the oil (assuming you're on a house shot) and based on your description of her game, not many pieces would react from there. Typical oil lines exist from 8-10 board on both sides of the lane so if she's throwing the ball into second arrow from the left within the first 40 feet, this could also explain her lack of motion/hook combined with her lower rev rate. The first test is to take that same ball and see if she can throw it straight down the 5-6 board area to see if there's any movement and that will tell you that there's friction/dry there. She may be just playing the wrong part of the lane. If she cannot play that far out, then you would need a stronger piece to roll or grab in the oil.
In regards to changing her style/release, tough thing to do unless you get her to practice a fair amount. I'd recommend to let her do what comes naturally (which appears to be the backup motion), nothing horrible with that so long as it is consistent to some degree. This game is about repetition and my personal take is to let people do what comes more natural for them so they can repeat it better (high backswing, low backswing, cranker, stroker...etc). Nothing is written in stone that must be or not be in order to be successful. We're also talking about helping her have fun, not trying to get her PBA card. Feel free to pm me if you have any other questions, thanks.
Oh, just caught something..."span just over 3 inches"...is she throwing a conventional grip? This would explain the lower rev rate...
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