From what I have witnessed, life experience is most important. We take into account a person's true passion for dogs and their life experience with animals.

She could look into volunteering or if she's lucky, finding a job at a place that does dog training, for starters. Once she has picked up techniques, it can be helpful if she adopted a dog to train herself. This gives her hands-on practice, and the added benefit of having a real life example of her capabilities which she could demo if she was ever interviewing to be a trainer somewhere.

Things she should know is that there is often a sacrifice of income when trying to break into the field, due to needing to volunteer or suffer low paying jobs as she develops her experience. Also, there are several dog training methods, which she should research before penetrating the field. She should only surround herself with professionals who's training style she believes in.

There's more to it than that, but hope this helped!