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I don't know how "lazy eye" effects someone being able to use regular sights, but I am familiar with cross eye dominance. It may be that she is trying to sight with the wrong eye. If you take her shooting again, have her move the handgun in front of her other eye, and see if that helps. The red dot may help her more though because it doesn't require lining up a front and rear sight.
I am not an ophthalmologist, and I don't play one on television.