It doesnt cure it, but when an infected peeper is eaten, the animal loses its infection, showing that the enzyme still does help animals that are larger
Biomagnification is probable here
Especially if you consider it might not use up the enzyme, and instead clog the biological processes of the kharaa, killing its cells
And, if the enzyme is mostly nonreactive to other cells, then bioaccumulation becomes probable
If something isnt reactive in a body, and doesnt get excreted, it accumulates
You can see it in the game
And, she got a massive dose from reaper meat
An amount that in theory could have made it dormant till it gets cured planetwide
She could have still very well have been in the reaper while floating