Her period became longer because of the IUD
Question

During Ramadaan, my wife went and had an IUD (“the coil”) inserted after her period finished, and her period became longer, so she did not fast for eleven days. After that it was proven that for four of those days the blood was not menses but irregular bleeding. What is the ruling on those days? Is there any expiation to be offered? What is it?.
Praise be to Allah.Firstly: 
If the period becomes longer because of the IUD and the bleeding follows on from the period, then it is all menses, such as if her period is usually seven days but increased to eleven days. 
But if the bleeding stopped after the seven days, and she was certain that she had become pure, then she bled for four more days that was different from her usual menstrual bleeding, and that was because of the IUD, then these four days are not regarded as menses, rather they are istihaadah (irregular vaginal bleeding). 
Similarly, if it is proven medically that the blood was irregular bleeding and not menses, then it is istihaadah. 
Secondly: 
If a woman does not fast when she sees blood because she thinks that it is menstrual bleeding, then it becomes clear to her that it was istihaadah, she does not have to do anything apart from making up the days that she did not fast. 
Conclusion: If it is proven that these days were not menstrual bleeding, then she does not have to do anything apart from making up those days. 
And Allaah knows best.