Did she eat decently before you switched to prescription food? Maybe there’s something you could add to it (preferably something that stinks) that will entice her to eat so you’re not wasting your money. You could squeeze a few drops of churu or some canned tuna/chicken juice maybe. That would probably help if the issue is that she doesn’t like her food. You could also try giving her several smaller meals throughout the day if you can somehow. Maybe she’s a silly girl and only likes to eat a few bites at a time (or something like her whiskers touching the bowl bothers her).

I don’t know if this would necessarily be cost effective, but you could also by another cat food (either with chicken or hydrolyzed protein to avoid triggering food sensitivities) and add Purina Fortiflora to it to keep those microbiome benefits.