Istihadhah can be minor or medium or big depending on the amount of the blood. In all these types of Istihadha, fasting is obligatory as well as Salaah, but after Wudhu for every Salah in the minor, or adding on Ghusl before Fajr in the medium or adding three Ghusls ; before Fajr and before Zohr, and befor Maghrib in the big Istihadhah.
Minor Istihadhah is when the blood does not fill the whole pad. In this case Wudhu is obligatory for every Salaah whether Wajib or recommended.
Medium Istihadha is when the blood fills the whole pad but does not leak out of it. In this case she must add one Ghusl before Fajr.
Big Istihadhah is when the blood fill the whole pad and leaks out of it. In this case she must add three Ghusls as mentioned above.