I know it sucks sometimes but parents usually have a reason for their actions. I don't think your mother is going out of her way to be mean. Yes you would keep it in your room, but it is still under her roof and in her house. Maybe don't get moody or upset (not saying you are, just saying). Handle the let down with maturity and tell her something like "that is ok, I understand mom. Maybe later down the road!" The big issue I've seen with parents saying no is the child showing lack of responsibility or respect towards the parent(s). So... I don't know the entire situation at your house to know exactly what is going on, but my suggestion is to just take it with stride, don't get mad or throw a fit about it, and just accept it and move on? Because maybe you just weren't meant to get a hamster right now? Your "dream hammy" may come later on in life and you were just meant to be together

Good things come to those who wait!