What is the ruling of the Sharia regarding excessive menstrual bleeding due to an IUD, its cessation, and then its return, and when is the legal state of purity (Tuhr Shar'i) in this case?

She must perform ghusl after the cessation of blood for the first time, after the initial three days. At that point, the woman is considered pure. If the blood returns after a period of purity, she reverts to being in a state of menstruation, and she must refrain from all that which a menstruating woman is prohibited from. Then she performs ghusl a second time when the returning blood ceases. Both blood flows are considered menstruation because their duration, including the intervening period of purity, does not exceed fifteen days.