
She had given her everything and done everything to have the emperor / being the most powerfull woman in their Empire. But became disillusioned with him when she realised that he cared for noone exept his lost love, this includes her.
So as she was dying and finding herself needing to rely on her enemy Fl, who she had wronged in many ways and yet Fl gave her a chance to get back at the root cause of it all.
I think she chose it was better for her Fl and the rest to win than the Emperor or the fifth prince.. who resembled the emperor the most in personality. (The reason the empress tested him and had spies on him was cause she felt he reminded her of the emperor when they were young). So she knew he must be in it for his own goals and sinse Fl hated them both way more than she hated the empress, the empress in a way respected her. This is proven in her end as she asked for but one thing and was granted it and died quietly after.

The empress is the reason the emperor was on the throne, her politicaly stable noble background was what made him eligable to compreat for the throne.
Just like Fl in her first life paved the way for the firft prince only to be betrayed, the empress did the same for the emperor. But his betrayal came after the marriage when he brought in his first love.
I think this is also why Fl is linient with the Empress as she can relate to her sacrifice, + the empress hated her the emperors obsession with her mother + the mother got the empresses first love.
Does anyone else feel like the empress gave up too easily especially with how hard she went all this time? Idk