Answered by Sidi Tabraze Azam
Question: Must the women in state of istihada take any means to stop the bleeding prior to praying?
Answer: Wa alaykum assalaam wa rahmatullah wa barakatuh Sidi,
The prayer as an excused (ma’dhur) person is performed out of necessity; therefore, we try to use whatever means we reasonably can to prevent the person from praying in an excused (ma’dhur) state; whether that is by doing something to prevent flow, sitting on the floor and praying and so on. [Birgivi, Dhukhr al-Mutahillin]
If she is able to stop the bleeding, by using something such as cotton wool or the like, then it is necessary to do so. If there is flow whilst standing, she should sit and pray; if there is flow during the prostrations, she would use head movements to perform them.
However, she would not pray lying down as this too is only allowed in a state of necessity. Therefore she prays as an excused (ma’dhur) person in such a case.
See this link for further details on chronic excuses: http://seekersguidance.org/ans-blog/2009/06/04/could-you-please-detail-the-fiqh-of-chronic-excuses-and-ablution/
And Allah knows best.