No matter how well intentioned, do not get a dog unless all the adults in the house are on board.
She's 14 years old. What happens to her dog when she's at school all day? Puppies need round the clock care when they're small and they can't be left all day. Is she going to come home straight from school everyday to walk the dog? And get up early every morning, no matter how cold the weather, how wet it is or how tired she is?
What about when she goes to university and can't take the dog? Or moves out into a flatshare that doesn't allow dogs? No way does a 14yo have the maturity to look after a dog. Who's going to pay the vets bills, the insurance, the jabs, the food, the flea and worm treatment? Who's going to pay for puppy classes, leads, collars, harnesses, chews, toys, beds?
Dogs are not cheap. Ours costs a fair bit - he's a puppy and chewed through two leads in a day a fortnight ago! He needs food, chews, interactive feeders, slow feeders, toys, collars and harnesses (plural - they don't last forever). Puppy classes cost £70 per 7 week "block" and they really need to go regularly for the first 12-18 months.
When she's at school or out with friends, what happens to the dog? Who's going to toilet train it and take it out in the middle of the night? Is someone going to watch it during the day or do you need to pay for a dog walker or daycare?
Please, please don't do it unless you're 100% on board. Dogs, especially puppies, are very hard work. They pee and poo everywhere, bite, jump and nip. They pull on the lead, dig in the garden, chew the furniture and rip up the carpets if left to their own devices.
Mine is nine months now and while he's incredibly rewarding he's bloody hard work and I couldn't do it if my husband wasn't completely on board with the whole thing.