Ellen,
I don't know how serious you are about your bowling game but the fact that you are on this forum tells me you are serious. Let me say that if you have any aspirations on becoming really good, you need to rid yourself of your backup ball and learn to throw a hook ball.
The main reason why the backup ball is so prevalent among women bowlers is because their arms are constructed in a manner that encourages a backup. The key to
rolling high games in bowling is to string strikes, something that is hard to do with a backup ball because of lack of power at the pins. A backup bowler shoots a lot of spares.
So if you decide to stick with the backup ball go ahead and have it drilled for a lefthander. You might even develop a reverse hook which is somewhat better than a backup but is a strain on the arm and is difficult to control.
If you decide to develop a hook ball here are some pointers:
1) get used to using the 2nd arrow from the right as a target to break the habit that a backup bowler has of using the left side of the lane.
2) In the stance, the ball should be held to the right inline with the shoulder with the wrist straight and firm. Overemphasize the hand position for a hook by having the thumb at 9 o'clock and the fingers at 3 o'clock(suitcase grip). If more exaggeration is required have the thumb at 8 o'clock and the fingers at 2 o'clock. The result will be a weak hook which is ok while breaking the backup habit. Once your arm is trained to throw a hook you can learn to throw a more effective hook using a more powerful hand position.
3) Make sure the pushaway is straight out from the shoulder. If you were used to holding the ball in front of the body instead of towards the side, the pushaway probably went to the right before dropping the ball into the downswing. If you were to continue to push to the right when the starting position of the ball is in front of the shoulder, the armswing will end up behind the body resulting in rotating the elbow inside out resulting in the backup again. Again push the ball straight out from the shoulder to initiate a straight backswing.
4) Watch the shoulder. If the shoulder drops too much, the elbow could rotate clockwise which we are trying to avoid.
5) While learning to break one's self of the backup ball, the inside of the elbow should be facing the body at all times thus keeping the thumb in a 9 o'clock position.