Originally, I wrote Azula as a member of Perseus's alliance and was not a hero/member of the UAC until one event that changed everything.
Okay, I think I finally found the main reason to why Azula joined the UAC.
Erik "Stitch" Kuzmin and his men betrayed her by taking away the USB that contains the location of every Overlord nukes.
Once that's fulfilled, Perseus ordered Stitch to tie up loose ends... That means getting rid of Azula. Ozai, seeing that she's of no use to him or Perseus anymore, agreed to the plan to get rid of her.
"Good. Это на один менее свободный конец."Stitch said, putting a hand around Azula's shoulder as the scene became tense.
"What?"
Erik/Stitch pulls out his pistol and shoots Azula on her abdomen, Ty Lee and Mai's eyes widened as they saw what happened and realised what was about to happen.
"No!"Ty Lee shouted.
Both her and Mai attempts to attack Erik/Stitch, but he only shot them in their stomachs. Once done, he puts the pistol away in his holster and grabs the USB off of her pockets. He then nods to his men as Azula grabbed Erik/Stitch's wrist.
"My...father...will...have your head..."Azula said hoarsely while Erik/Stitch has a disgusted look on his face.
"Ozai was right about you being a dissapointment."He said before shoving her off as he ordered two Perseus Operatives to throw her body off of a ditch.
"Area santised. All targets destroyed."
"Solid copy, no movement detected. 2-6 going into holding pattern."
The two Perseus Operatives then carry her body off and threw it off a ditch along with Mai and Ty Lee's unconscious but wounded bodies.
"It's done, Comrade Kuzmin. What now?"A Perseus Operative holding an FN FAL asked.
"Let the worms feed on her body. No one will mourn her... Let's move."Erik/Stitch said, before he turned away along with his men. A Perseus Operative throws a lit cigar at Azula's body.
The last thing Azula sees is Erik/Stitch's helicopter flying off before her vision turns black.