You've done an amazing job by just giving her a better place. A lot of people may frown upon this but maybe live food like feeders? I know a lot say they can introduce parasites but at this point it could be a turn around for a good deal of protein and a predatory feeling for her to search a coiple feeders down. ( I honestly feel bad saying it sorry ). I had a large 7" oscar in a 55 back 35 years ago and that was its staple food. cause I had a 10 gallon under the 55 so I would get 2 dozen and have to do that every 2 weeks at the tune of $.05 per feeder sorry
I don’t think there is anything wrong with it. I hear Oscar’s really like earth worms so that may be a great place to start. They sell red wigglers and night crawlers both at my PetSmart.
Maybe get some tongs and hold the red wigglers near her mouth? The movement might entice her to eat.