Many years passed, and King Al-Mu‘izz was stable on his throne; and Sayf Ad-Deen Qutuz became his most prominent leader, known in public and private. The role of the wife and old queen, Shajarat Ad-Durr nearly disappeared. This, without doubt, enraged her with resentment, and King Al-Mu‘izz also reciprocated hatred for her, for he knew well that she had married him only to be able to rule Egypt through him. But even, life has its ups and downs.

In 655 A.H., after seven years of rule by King Al-Mu‘izz, he wanted to fix his footing more firmly in office, and more and more he wanted the neighboring regions of Shaam and Palestine. But since he had insufficient power to realize his dreams alone, he had to become allied to one of the great emirs in the region to help him do so. Nevertheless, in view of the fact that breaking treaties was usual at this time, he liked to consolidate the alliance with a strong bond, i.e. marriage.
King Al-Mu‘izz chose the daughter of the treacherous emir Badr Ad-Deen Lu’lu’ of Mawsil, whom we talked about so much, and referred to his disgusting cooperation with the Tatars.

Learning about that, Shajarat Ad-Durr burnt with jealousy, and was given to anxiety and agony and thought that if he married this girl, her page would be entirely removed from history. Her jealousy blinded her from discretion and calculation, given that she was recognized for her wisdom. She did not know that the Bahri Mamluk leaders had disappeared, which means that real power came in the hand of the Mu‘izzi Mamluks who were entirely obedient and loyal to King Al-Mu‘izz ‘Izz Ad-Deen Aybak. She indeed miscalculated the matter, and decided, with feminine emotion, to do a speculative act, even though it was familiar to her, since she had previously done it with Tooraan Shaah, her son-in-law, and would do it now with her present husband; i.e. to kill her husband, King Al-Mu‘izz. Let him be killed then, whatever the consequences might be. That was what Shajarat Ad-Durr had in mind.

https://www.islamstory.com/en/artical/20811/shajarat-ad-durr-burns