I’m glad she’s been to the vet, and in the meantime you can look in your town directory for “exotics” vets. They specialize in bunnies. Also, check the top of the Q&A forum for pinned posts about finding a vet.
GI tract problems are common and serious for bunnies, so it sounds like she’s just too young and alone to be successfully weaned and eating normally. I agree that the veggies are too much for her. Definitely hay, in case she has some blockage. Only one, very mild green like green leaf (Never iceberg lettuce) would be OK to try slowly, in very small quantities. Every time you switch to a new veggie, it can upset a bunny’s stomach, so just cut way back to hay, maybe the one green, and simple pellets. You can try a pellet slushie, where you soften the pellets with water so it’s more mushy for her to eat.
But the vet needs to handle this crisis for now. By all means call an exotics vet for a second opinion.