issue with fuel filter would likely be constant. and don't bother with fuel additives. they help keep things clean, but can't clean things once they're dirty. additives have no *corrective* abilities, save fuel dryers and stabilizers. purdy much all the fuel out there has that stuff in it anyway.
i'm thinking she just needs a general "physical" cleaning of induction sensors, injectors, and emissions systems.
reading trouble codes could be of help. not all trouble codes prompt a light. per manual.
so either take it to your local shop or and have them inspect/clean those, or
DIY,
use solvent or seafoam for a cleaner.
location of sensors,
http://www.autozone.com/autozone/rep...geName=Corolla component locations-1.8L I4 MFI 1ZZ-FE VIN R
how to service them,
http://www.autozone.com/autozone/rep...96b43f80380304
i would pay special attention to the "idle air control" valve and "egr" valve.