Are you a responsible person? Pick up after yourself and others! Do your chores and ask her what else needs done. Make a contract with her. You show her how dependable you are for say six months and then you get a dog. Prove yourself! Save your money for the adoption fee and vet bills. Research your costs. They need heartworm pills and flea/tick meds every month! Plus shots. Food. This is serious stuff you need to consider! Still want a dog? Prove it. Good Luck kid!
Help her around the house and do chores. I just got guinea pigs and first my parents said no but my sister looked anything and everything to know about guinea pigs. If i were you i would ask questions about dogs and write it down on paper showing your mom your responsible. Make sure u make a list of what you will do when you have it and where you would buy the dog. I recommend Mspca or pet finder :) Good luck!
Do your chores good and show her you are responsible.hopefully she'll see you being responsible she will let you have a dog. Dogs will make a mess and she probably hesitant on getting one. You have to let her know you will be responsible enough to care for one