Wait for as long as your menstrual period normally stops you, and then take a ritual bath

Istihādah (vaginal bleeding outside the menstrual period) is: when a woman experiences an incessant flow of blood after her usual menstrual period is over.
A woman experiencing Istihādah should consider herself menstruating for as many days as her menses would normally last before starting to have Istihādah.
If the number of days of her normal menstrual period passes, she is considered pure from menstruation - even if she is bleeding of Istihādah - and should take a ritual bath.
A woman experiencing Istihādah is not required to take a ritual bath for each prayer because the female Companion (may Allah be pleased with her) would take a ritual bath based on her personal reasoning. Had it been obligatory, the Messenger of Allah (may Allah's peace and blessings be upon him) would have made it clear to her.
A woman experiencing Istihādah is required to make ablution for every prayer because her Hadath (ritual impurity) is incessant, and this applies to every person whose Hadath is incessant like the one who suffers from incontinence of urine or continuous passing of wind.
Asking the people of knowledge about confusing religious matters, as this woman complained to the Prophet (may Allah's peace and blessings be upon him) and asked him about the excessive bleeding she was suffering from.