How do I get my mum to let me get a dog?

I really want my mum to let me get a dog!!! But she is not letting me get one! I think that is very mean of her!! I only have 4 cats, 7 turtles, 1 frog, 8 bunnies, 2 canaries, 1 macaw, and 6 guinea pigs..that's ridculous! Why won't she let me get one?? Ugh! All my mates agree that she is the worst mum ever! How can I convince her??? Help me!!