Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
A woman is not obliged to use an absorbent such as a piece of cotton or anything else in her underwear during prayer. You have been informed incorrectly. However she has to take these precautions if she suffers from prolonged bleeding or any continuous vaginal discharge; in this case she has to pad that place with a cloth or the like.
The same ruling also applies to a man if he suffers from incontinence of urine or the like. There is no difference between a man and a woman regarding this matter.
Allah knows best.