All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
As long as the total number of the menses' days does not exceed fifteen, all the fourteen days in which you see blood in any color are considered from your menses. That is because the lengthiest duration for menses is fifteen days. So, if the woman experiences days of menses more than her usual habit, these days are considered from her menses, too. As such, you should take a ritual bath after your purification from menses, that is, after the stoppage of blood on the fourteenth day and you should then observe the prayer.
Allah knows best.