Maybe you can try to convince your mother to keep the snake. As many of us snake owners know, snakes are not like dogs who are constantly on the move and hyper animals. Hiding and appearing to be bored (to us humans anyways) is normal. The snake is getting its every need met from you (that it may not get from someone else), I say that's what it's getting from you >> a healthy, happy life, what more can a snake ask for (assuming it's taken care of properly)? And you are getting enjoyment out of owning the snake and learning to become more responsible. Mutual beneficial relationship. Maybe if other members contribute, you can show your mother that your snake's behavior is normal and that it isn't being deprived of anything. I agree, don't take it back to Petco, and heaven-forbid don't let her throw it outside!

But if you are forced to rehome the snake, I'm not much help. I have never sold/rehomed online before.