Technically, rayquaza should be in the ozone layer, which doesn't necessarily mean hoenn specifically. Though, who said there isn't more than one rayquaza.
Is there any dragon-ish thing in Hoenn?
She could request to study under Drake of the Hoenn Elite 4. Then there would obviously be myths/legends she could learn about, regarding Rayquaza, Latias and Latios.. Plus there's a large amount of Dragon Tamers for her to battle and learn from..