Remove Ada and Leon dies
Simple as that
Ada's storyline doesn't drive the plot forward, she reacts to it. she s a recurring catalyst who intercepts the finish line after the main characters do the heavy lifting to move the narrative forward.
If you remove Chris, Leon,Jill or Claire, the story collapses. If you remove Ada, the bioweapons still exist, the outbreaks still happen, and the plot still functions, she just isn't there to profit off the fallout, other character will. The main four are irreplaceable narratively speaking, she actually is.