Purity: Change in Istiḥāḍah Intensity During Prayer
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 419:
If during prayers the medium istiḥāḍah of a woman becomes excessive, she must break her prayer, perform ghusl for excessive istiḥāḍah, do the other things required of a woman with excessive istiḥāḍah, and then perform that prayer; and based on recommended precaution, she should perform wuḍūʾ before ghusl. If she does not have time to perform ghusl, it is necessary for her to perform tayammum in place of ghusl; and if she does not have time to perform tayammum either, then based on recommended precaution, she should not break her prayer but instead complete it in the state that she is in; however, it is necessary for her to make it up after its prescribed time. Similarly, if during prayers the slight istiḥāḍah of a woman becomes excessive, she must break her prayer and do the things required of a woman with excessive istiḥāḍah. Based on obligatory precaution, the same rule applies if the slight istiḥāḍah of a woman becomes medium.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)