She had to accept Felix won
Ladybug was understandably very angry when Felix resurfaced in "Emotion" at the Diamond's Dance, seeing as she and Cat Noir have been searching for him ever since he handed over all the miraculous in the miracle box to Monarch back in "Strike Back".
Losing all the miraculous to Monarch was a major blow for Ladybug, the sacrifices alone she had to make to ensure the safety of the magical jewels took its toll on her the more they grew over time, leaving her no other choice but to even sacrifice her own relationships(temporarily) as well as her own peace of mind. No one understood just how hard she worked to keep Monarch from taking the jewels from her, even spending many sleepless nights creating plans to prevent a future possibility. However, the one thing she never considered, was someone other than Monarch, Felix, taking all the miraculous.
("Kuro Neko" and "Destruction", we are shown that Marinette would spend many sleepless nights crafting plans to ensure the safety of the miraculous)
It was only natural for Ladybug to assume Felix was working alongside Monarch, given he had previously attempted to form an alliance with him back in "Felix", rather than side with the heroes. But through every encounter they had with Felix, his motives have always remained a great mystery, including too Adrien, who grew up with Felix.
(Of course Felix worked alone and never planned to work alongside Monarch, he was merely a crucial part to his plans of obtaining the peacock miraculous(more here). )
Ordinarily, Ladybug was used to taking the time to understand her enemies, it was because of this level of understanding she developed over people like Monarch and his akumatized villains, that allowed her to figure out their next move and plan ahead. Although Ladybug believed Felix was no different than Monarch if he resorted to manipulating, deceiving and leaving others to suffer the consequences of his decisions, she could never truly understand who Felix was. She couldn't plan ahead and figure out what his next move would be, leaving her to only wonder why he did everything he did despite them posing no actual threat to him.
( Ladybug could not understand Felix.)
Felix said he had plans to create a free world where no one would be excluded like he was, where no one would fall under anyone's control and be forced to abide by what others thought was right and wrong.
Of course listening to Felix's reasoning for wanting a free world was the last thing Ladybug ever wanted to do, he was after all, the one who made her lose everything, not just the kwamis and the miraculous, but faith in herself, along with the faith many people had in her. After losing all the miraculous to Monarch, Ladybug could not trust herself to be the guardian and the protector she promised to be for all those in Paris back in "Origins part 2". Worse yet, some citizens did not hesitate to proclaim to the world how much they believed Ladybug was not capable of being their protector, preferring to focus on the consequences of Monarch obtaining so much power from her one mistake, rather than look back on everything else she had done for the public that proved she was fit to be their hero.
(In "Determination, Ladybug was hesitant on making choices amidst a fight, believing there was reason to doubt herself and whether or not she could make the right choices.)
Such a defeat from Monarch and such cruel words from the public, left Ladybug in a constant state of indecision, wondering if her choices over a matter would truly solve a problem or just make things worse, just as much as it did when she believed it was the correct choice to trust who she thought was Adrien (who was really Felix) with the dog miraculous back in "Strike Back".
Of course Cat Noir was there by her side to help her remember what she was capable of, but that level of doubt she had over herself was not something she could ever truly stray away from, because unlike most people, her decisions decided the safety of millions. Facing Felix in "Emotion" gave her the opportunity to finally confront the person who left her with so much loss, but amidst being consumed by her own emotions, angered at everything Felix had done, she forgot that what she was searching for in a fight was not revenge, but a solution.
To Ladybug, the solution seemed obvious: use whatever her lucky charm gave her to help piece together a way to win against Felix, allowing her to take back the peacock miraculous and in turn undue everything he had done. But when the time came for her to rely on her abilities and use her powers of creation to find the solution that would lead the way to the victory she hoped to obtain, to her surprise, her powers gave her nothing.
In all her time as a hero, Ladybug had never been in a battle where her powers of creation left her nothing, she had never been in a situation where she could not do anything to piece together a way to solve a problem that at times even seemed hopeless to solve.
Every problem has a solution, those words always resonated within Ladybug and everyone that knew her, but by being faced with a problem she had no chance of taking action against, left her realizing something she never thought to consider, which was that there was a solution to the problem in front of her, it just wasn't what she was hoping for. Her lucky charm gave her nothing, because that was exactly what she needed to do, nothing.
(Ladybug understand what the lucky charm was trying to tell her)
Alya always said all that is necessary for the triumph of evil is that good people do nothing. To save the day against evil, Ladybug felt it was only right to do anything and everything she could to win for the sake of others. Doing nothing was never something she thought she would ever have to do, but she had to, because as much as she wanted to believe Felix was the evil one who needed to be stopped, to know that the only solution was nothing, left her wondering if she even knew what winning actually meant, now that her own plans of winning against Felix were not going to turn out the way she had hoped. As much as Ladybug wanted to win, it became abundantly clear she was NOT the one who was meant to stop Felix.
It pained Ladybug to admit it, but she had to accept she could not win against him, she could not take back the peacock miraculous and she could not undue what he had done, but she could still accomplish what she knew she could, and that was find a solution. After her lucky charm told her to do nothing, Ladybug could only focus on one thing and one thing only, Felix. Felix wasn't just the cause of the problem, he was also the solution.
(The only one who could put a stop to Felix and everything he had unleashed onto the world, was Felix. )
Despite learning about his intentions to create a free world, Ladybug still couldn't understand why he wanted such a world due to one very crucial piece of information she did not yet know about him, and that was the fact that Felix was a senti human born from the power of the peacock miraculous, who had spent a lifetime being denied the freedom to live and make his own choices on what he wanted to do in his life.
Felix spoke of freedom and how much he wanted his new world to revolve around being freed from the control of others, but if freedom was all he wanted, then that's all Ladybug could leave him with. Ladybug had to leave Felix the freedom to decide if he wanted to stop himself, and if winning wasn't what she thought it would be, then chances are, it wouldn't be for Felix either, and it wasn't.
(Ladybug leaves Felix with the freedom to make his own choice.)












