It would be helpful to see a photo of your setup. I'm assuming that this ball python is probably close to a hatchling size? Do you have a scale to where you can weight it in grams? Personally I would never assist feed, have you ever done this before? It usually makes the snake very stressed and can cause them to go off of feed even more. I'd suggest finding a pet store that has live pinky rats and put a rat in it's cage in the evening and I can almost guarantee that by morning it will be gone. A live pinky rat with it's eyes closed is perfectly safe to leave in there overnight. Any other live rodent needs to be checked after about 5-10 minutes and removed if not eaten to prevent the rodent doing damage to the snake (i.e., a small mouse).
PetSmart needs to stock some live pinky rats to feed it's ball pythons if it intends to take care of them properly. Or at least outsource it, have a real breeder come in after hours and drop in some pinky rats if they don't have the stomach to do it themselves. Getting the weight of the snake in grams is helpful, you should feed a rodent that is about 10% of the weight of the snake, usually 5% - 10% is the rule of thumb. So for a 100 gram snake you should feed a 10 gram pinky rat. A small snake like that should be fed every 4-5 days. I usually feed small snakes on Sunday and Wednesday, usually 1-3 rodents back to back (multiple smaller rodents or one larger rodent). If I have an excess of rodents in my rack I feed the smaller ones off in larger numbers to balance out the rodent population. If you feed a rodent that is less than 5% of the weight of the snake it may not see it as a food item and may refuse to eat it (i.e. a pinky mouse)