How Can I Convince My Mom To Let Me Get An Indoor Dog?

I want to get an adult purebred dog. (I’m 16, but I haven’t got the energy for a puppy). My dad’s fine with it, and we’ve GOT the money to buy one from a proper breeder. (My dad bought me a brand-new Lexus for my birthday, and I asked him if I could have the dog. He knows what they cost, and he said yes) ( I want a Yorkie or a Cavalier, maybe a Papillon) The only thing standing in my way is, well… my mom. We’ve always had large, mixed breeds OUT in the backyard, but my mom won’t let me have one indoors because she thinks they’re “dirty”, because “they go to the bathroom wherever they happen to be”. And we have a cat in the house! And she’s always getting cat litter all over the bathroom floor, and she DOESN’T THINK ANYTHING OF IT! Does that make ANY sense? How can I convince her that dogs are no dirtier than cats, and that they’re fine with the potty business once they’re grown-up and house-trained?