As someone who worked with horses for 6 years (and has horses now), who has 2 sisters who worked with horses, and who has a 16 year old horse-mad and very talented daughter, I would really try to persuade her, like others above, not to work with horses. It really is very hard work, long hours, few days off, not great pay, and bosses can be a nightmare. Often you get to do all the hard work, mucking out, poo picking etc, with only the less exciting riding, and getting to compete is rare. There are no doubt some yards where people get amazing opportunities, but they do seem few and far between. There are so many youngsters wanting to work with horses that employers can be very choosy, and really don't need to look after their staff well.
Training as a vet nurse, farrier, vet, nutritionist etc is worth looking into, or getting any other well paid career so you can buy your own horses and do your own thing, is, in my opinion, the best way forward. I really loved parts of working with horses, but other bits were awful, especially the way girls were treated (this was 25 years ago now, but sexual harassment was just part of the daily routine, often physical), plus we really were 'disposable'.
Good luck x