The Mutawassitah
A woman with istihazah mutawassitah has to change the sanitary napkin, perform wudu' for every salat and perform in addition a ghusl before the dawn prayer.
If the medium bleeding of istihazahstarts after the dawn prayer, then on that day it is wajib on the mustahazahto perform a ghusl before the noon prayer. And if it starts after the noon and afternoon prayers, then it is wajib on her to do the ghusl before the evening prayer.
If the medium bleeding of istihazahstarts after noon prayer (and before afternoon prayer) or after evening prayer (and before night prayer), then it is wajib on her to perform the ghusl before afternoon or night prayer.
In the same way, if a woman sees istihazah mutawassitah before the dawn prayer and does not perform ghusl, then she has to do ghusl before noon prayer and repeat her dawn prayer after the ghusl.
Adopted from the book : "The Ritual Ablutions for Women (Taharatu N-Nisa')" by : "Sayyid Muhammad Rizvi"