Hello and welcome to FF! Sorry about the juvie injured NTF . Wondering if your city has a law that does not permit the veterinaries to treat it? Sadly, without an x-ray it's impossible to know what is the internal damage to frog.

Topical antibiotic should help prevent the wound from infection. You could also use Melafix (an aquarium medication) on the water area (mix according to bottle label) to help reduce any bacterial issues.

Pedialyte soaks will also help keep electrolytes balanced and frog hydrated. Rana species are very shy and easily stressed; so that is the challenge you are facing. A larger quarantine set-up with hiding places could help frog feel safe and lower it's stress levels and maybe start eating again. Besides insects, you could try offering earth worms like not dyed Canadian Night Crawlers (from Walmart or a local bait shop). If frog is small, you can cut worms from pointy end about same as the frog's mouth to vent length.

Because it's unknown if frog has additional internal injuries; handling or force feeding are a big risk. Hope this helps and good luck !