How old is she?  It's just a habit, she'll naturally gravitate towards it.  Kids definition of effort and our definition of effort are often two completely different things.  Kids won't really try to do something, they just decide they're going to do something and act like it should just happen.  It's like my daughter and the high school bowling practice.  They don't practice otherwise, and when they're at the bowling practice, they all just horse around, they just throw shots around chatting up teammates and playing on their phones.  Then when the meets come, all the sudden they decide they want to do well and act like it should just happen, naturally getting upset when it doesn't. 

Longwinded point, but breaking a habit is hard either way you look at it.  You really have to break it down and isolate the release.  If she's doing her full approach and then watching what the ball does on the lane, that's way too much going on for her to just focus on how she's letting go of the ball.  I'm willing to bet she's just not REALLY focusing on how she's letting go of the ball.  Help her to get a feel for what a correct release feels like, because sometimes it's hard to do something if you don't know how it's supposed to feel, like if you were told to take a trimmer and make a straight line across the back of your head without a mirror. 

The way women's arms are built as well naturally make them tend to automatically throw backup balls, that's why so many of them do it starting out.  Another thing is expectations.  A lot of bowlers for some reason expect things to just happen.  She's got a habit developed, it's going to take a lot of hours to turn it around, it's not like, "oh, just turn your arm the other way," and it's done.  It will save you and her a lot of frustration if you take a more patient approach.  I'm not saying you're expecting it to change overnight, but just keep that in mind if it takes her a while to get it. 

If a man holds his arm out straight in front of his waist, his arm and forearm will stay straight and if a woman holds her arm the same position her arm will go to the right from the elbow. Just like Gizmo stated the way women's arms are built. Many of the
women have weak wrist and this promotes the backup ball. Any change in a bowlers
game takes a lot of work and realize that they may have to regress sometimes before they can move up to their goal. If your daughter does not have a bowling glove, with the metal plate to keep the wrist straight. Sometimes this is a great bowling tool to keep the wrist in the proper position at the release point.
jodyk24

First off, throwing a backup ball is a function of swing and mostly release - so don't confuse the issue by telling her to do ANYTHING in a full approach.

This should be tackled by isolating the release, then the arm swing, then incorporate it into the swing....meaning a swing drill (usually done on one knee), then the 1-step drill, then back to normal approach. Make sure she drills the motion into her muscle memory before taking the next step.

The football method can help conceptualize the motion of the hand to create a hook/roll but also you can have her make the motion of holding the ball and have her thumb pointed at the pins throughout the whole swing (which forces the fingers to the outside and thus prevents a backup ball - which is the thumb going away from the body to the 2-3 oclock position at release).

Billy,

If you're still in Spartanburg get in the car for an hour, you won't find better than this.  He's got shops in Gastonia, Rock Hill and Columbia.  I'm not sure where he does lessons out of.  You'll need to catch him when he's home. 

Chuck Gardner 

Email: chuck.gardner@brunbowl.com
Day: (704)519-7712 
Evening: (803)324-2255 
13207 Pine Harbor Rd 
Charlotte , NC 
28278

I do coach high school and have a young man that throws a back up ball, he's right handed and had an accident when a young man and cannot roll a ball like a typical right handed bowler. He balls very well and is improving all the time.
I'm from the Dayton area and a young lady (adult now) was just been named to the Ohio State All Star Team who has thrown a back up ball her whole life. Her dad is a well respected college coach and never tried to change her approach to the game as she averages about 220 with numerous 300's and 800's. Sometimes it is what it is and work on what is natural for her. If she is right handed have her equipment drilled for a left hander and make sure the ball driller is well informed of what she does.
Work to her strength and what comes easy for her.

Hurt wrist might not be strong enough...

That's a good point too. A wrist brace might need to work alongside re-learning the swing.

When a righty hooks the ball like a lefty or vice versa, or maybe better explained as saying they make the ball hook the "wrong" way. 

Here comes the idiot question of the day,

What is a backup ball?