How to persuard my mum to have a dog?

Shelties are WONDERFUL!
%%%First of all check out three books from the library about dogs and dog training. When talking with your mom, just bring up casually something that you just learned from the books.

%%%Ask her if you can volunteer at your local shelter to help dogs, and learn more. (most shelters have a petting room, or a dog walking program, and need volunteers to just give animals attention)

%%%Study the books about choosing the right breed for your family, and comment on this often to her.

%%%Ask if you can give a dog from the shelter foster care for a week to see how a dogs fits in your family

%%%Do ALL chores as soon as asked

%%% Keep your room clean, and show that you are growing up and accepting responsibility.

but you need to remember that dogs live to be 12-16 years old, and you can't know where you will be by that time.

.Dogs don't stay puppies very long, and taking care of an old dog is expensive and time consuming...so who will be there for the dog?? Most likely the duty will be left for your mom.
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also, during the weeks of potty training, it is Mom's furniture and flooring that will be ruined..and her table legs that will be chewed..
It will never work if she doesn't want the dog in the first place...

If you can do all of the above, and let your mom know how much you understand all of the problems that come with a dog, she may be willing to consent....but, you really do need to consider her feelings and wishes.

I believe we would first need to know her reasons for saying no??

First, make sure you are really - really - able to afford it. A dog can cost $600-$1000 in the first year alone depending on the breed and where you live.

The best thing to do would be to find out exactly, and I do mean exactly, why she’s against it, and base your argument around that. The thing is, it will be difficult. Your mom is really going to have to be on board with you here. She’s going to take care of the dog while you are at school (unless she has a job, then it’ll be all alone all day). She’s going to have to cover unexpected medical expenses, which can be hundreds if not thousands of dollars. She’s going to have to buy the food every few weeks, and pay for any damage it does to your house. Her carpet will have stains all over it. Will she like that? No matter how careful you are, there will be accidents. She’s going to be involved with the dog - a lot - and if she doesn’t want to get it, then it might not be smart to push her. The dog will suffer, and your relationship will suffer.

tell her you will take care of it. When I asked my Mum for a dog, she said no because we have too many cats. I told her I would get a puppy so that he would adapt to all of our cats, and he did. Thinks he is a cat. But anyway, your situation is different than mine. if your problem has anything to do with the care of the animal you need to show her that you can take care of everything by being more responcible around the house. If it is allergies I cant help you. but look up this breed of dog and come up with a pro and con list for her. show her the monthly cost of dog food and shots. show her you care enough to do research.