If your daughter doesn't have Strabismus or squint eye, continuous usage of spectacles is sufficient for her visual system to keep developing normally, and patching is not required at all. Make sure to confirm with your Ophthalmologist if your daughter has any form of squint.
The refractive error is not curable, it is more like a measure of your daughter's eye than a disease. As she is still young, this number is likely to change frequently as she grows older. Make sure she gets her eye exam every 6 months for a few years, and then yearly later.
As for the diet, a balanced diet, green vegetables preferably in salad/uncooked form, fruits, dry fruits like walnut are rich in vitamins and minerals needed to keep the eyes healthy.
Next Steps
Rule out squint, by consulting an Ophthalmologist, if not present, patching might actually be harmful.
Health Tips
Make sure she wears her spectacles regularly, as not wearing them might lead to Lazy eyes or Amblyopia.