She had an operation on her uterus

A woman may experience something that causes her to bleed from her vagina, such as an operation on the uterus or close to it. This falls into two categories: 

1 – If she knows that it is not possible for her to menstruate after the surgery, such as if she has an operation to remove the uterus altogether (hysterectomy) or blocking it so that no blood can come from it. This woman does not come under the rulings on istihaadah (non-menstrual vaginal bleeding); rather she comes under the rulings on one who sees some yellowish or brownish discharge or some wetness after her period ends. So she should not stop praying and fasting, or refuse to let her husband have intercourse with her, and she does not have to do ghusl in this case. But when she wants to pray she should wash the blood from herself and put a piece of cloth or something similar over her private part to prevent the blood coming out, then she should do wudoo’ and pray. She should only do wudoo’ after the time for the prayer has begun, if there is a specific time for the prayer such as the five daily prayers, or when she wants to offer a naafil prayer. 

2 – If she knows that there is no reason why she should not menstruate after the operation and it is possible that she may menstruate. This comes under the ruling of istihaadah and is indicated by the words of the Prophet (peace and blessings of Allaah be upon him) to Faatimah bint Hubaysh: “That is a vein and is not menses. When the time of menses comes, then stop praying.” The words “when the time of menses comes” indicate that the ruling on istihaadah may apply to one who has a period that comes and goes. If a woman does not have a period then her bleeding is regarded as coming from a vein in all cases. End quote.