yes, the muscles get stronger as they develop and the snake learns how to control it more. but their muscles are used more for constricting prey or for their movement. their muscles help move food down their esphogus, but it doesn't force it down (and it def doesn't compact it to a nice, smaller size). that is why they will regurge if the prey is too big. unfortunately i'm afraid if this poor snake is having trouble passing mice fuzzies, it will continue to have trouble. it sounds like prey has to pass the kink to get to the stomach and i would be afraid of the snake choking b/c of the added Spider derp/wobble as it tries to pass the kink before it can spit the food. it would be a lifetime of care observed and assist feeding. and w/ the wobble, depending on severity, there would be alotta corkscrews and barrel roll type movements and times when u check on your SPider and u think they're dead b/c their flipped over but really that's how they sometimes like to coil/sleeping upside down.
the owner can give it a good fighting chance but has also has the responsibility (w/ feedback from their vets) to know when one or both (owner and/or animal) are at wits end. i know a guy that had to put down a Panda b/c of a kink. can u imagine how that feels? ugh. but i'm glad that u work w/ vets and have experience in both the healing of animals, their end of life and counseling their owners. that last part is undervalued and can be just as important in animal care.