她离开了三年了 vs. 她离开三年了 Is there any difference between the two?
她离开了三年了: She had been away for 3 years. (She could have been back now or could have not been back.).
她离开三年了: She has been away for 3 years (have not been back). 

她离开了三年了 could be the abbreviated version of 她离开三年了 and is used to describe the same thing, and it could also be different.