I second the advice about blood ketone meters, but you really do not have much to worry about. Ketones develop only when there is no insulin (or not enough insulin) in the body to transfer glucose into cells for energy use. If you're injecting her with insulin and she's responding to it (as the lows indicate), then the insulin is available and she is not producing ketones.
However, other conditions can lead to fruity breath. Has your daughter been losing weight? Has she ever been tested for celiac?