Even as a joke, you were still faulting her for the situation. If it was a return from earlier that day, it is possible she was not even over at the reptiles yet to notice meaning it is in no way her fault. It could be someone else's mistake for being distracted (with enough customers, being distracted can be easy for young kids being paid minimum wage), but it is still a mistake. I doubt they flat out don't care about the snake; it was just temporarily forgotten by the employee who received it in indeed it was a return. There are a million scenarios that could have happened, but what is known is that it was a mistake and it was promptly corrected. Therefore I think you're being too harsh.