All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The water which that woman saw before Thuhr prayer is not postpartum bleeding, because postpartum bleeding is the bleeding that comes out after giving birth to the baby.
As regards the obligation on that woman to make up the Thuhr prayer, then the scholars differed in opinion about it. However, the correct opinion is that she is not obliged to make up that prayer because a woman who has her menses or postpartum bleeding during the time of a prayer, is not obliged to make up this prayer according to the correct opinion of the scholars but it is better for her to make it up in order to be on the safe side.
It should be noted here that if a woman sees this water before giving birth, and then the time of the prayer starts, then she is obliged to perform the prayer because she is Islamicly required to perform it. This water is not a sound reason for her to abandon the prayer because it is neither menses nor postpartum bleeding. When she wants to perform the prayer, she is obliged to perform ablution after the time of the prayer starts exactly as a person who has incontinence of urine and the like does.
Allaah Knows best.