Why don’t we hear Qatam bint Taymiyah role being discussed in the Murder of Imam Ali (AS)? Is her story true?

Yes. It’s true. Ibn Moljam fell in love with her. She was very beautiful. She hated Imam Ali (a) and told him she’d marry him if he kills Imam Ali (a). He also hates Imam Ali as he was a Kharijite. Mu’awiyah also helped him kill Imam Ali. So Ibn Muljam struck Imam Ali for a number of reasons, and Qutam was one of them. She wasn’t the sole reason, but one of the reasons.