Get a new vet, and give the poor baby a LIVE rodent as big around as the widest part of the snake. That is the rule of thumb. For a baby ball, that is usually a fuzzy rat, or hopper mouse. It's important not to handle her, and to get her feeding asap, hatchlings can go downhill fast without food.

Forget the meds they gave her, if the sole purpose is to stimulate her appetite. These things don't work. Verify first that this was the sole purpose, and it's not a medication for something actually diagnosed, such as an infection or parasite infestation (which would have required a fecal exam to detect, so if you didn't give the vet a fecal sample, the vet should not be de-worming your snake). I would ask what the vet actually gave her. I worry your vet may have given her something stupid like an injection of flagyl--antiparasite meds can add stress to the body of an already weakened snake. Hydration is very important--get your humidity levels up to 60 to 80% and make sure the snake has fresh water at all times. Hatchlings can dehydrate easily. Make sure the cage has a 90F basking area and is 80F on the other end--this gradient is very important. Use a thermostat if you need to, to keep the temperatures stable.

I personally would consider your little snake to be in serious condition, and perhaps worse for some of what the vet may have done to her. Force-feeding is terribly stressful for snakes. Wait 5 days after a force-feeding before offering her food again.

www.arav.com is a good place to find reputeable reptile veterinarians. Bad vets who don't know reptiles well can kill even a healthy animal with bad advice. It's less common these days, but it still happens (clearly). Any vet who thinks a live fuzzy rat can harm a snake is not a vet you should be using.