Tell your dad that horses are cheaper than a therapist, bail or hiring a lawyer. You will be so busy at the barn and on weekends at horse shows that you won't have any time to get into the usual teenage mischief.
There are too many advantages to cover. Over all you will just be a happier, fitter more compassionate person. Horses require us to be true partners, to listen and talk, in order to get their best just like people do. Barns are very social, Horse people are very social, but also have a strong sense of morality, fairness and ethics. Not a bad place for a young lady to be.
On the negative side horses are Hard Work. They rely entirely on YOU for all their care, it is up to you, once you take on that responsibility, to ensure that they are healthy, happy and comfortable. This often means putting their needs before your wants. It means self sacrafice, commitment and self discipline. A horse is not like a Toyota that you can park in the garage and forget. It is a living breathing creature that will be alive and need care every single day for about 30 years.
Are you prepared to take on that respondsibility?