It's certainly not a stupid question!
Yes, if the growth is even around the hoof wall, and her hoof is staying at an angle appropriate for her, matching her legs/conformation, then she is balanced and her hoof is quite happy.
The hoof grows in response to each step she takes, and the type of ground she's on. If you have been riding on softer grounds and decide to do some heavy riding on more abrasive grounds one day, the hoof will wear a little faster.But, it depends on how drastically harder the ground and ride is. That would be when boots are handy as a back-up, that occasional ride you take that's farther and harder than normal. But if you ride on gravel all the time, her feet are likely to be well conditioned for just about anything, or if she lives on rough terrain, her feet are conditioned for you in her pasture time.
Of course, just so nobody mis-interprets me, the horse has to move around in his turnout time on the hard ground for it to do any good, and the proper diet is another main factor...
Anyhoo, back to the question, if you don't go on extreme rides out of the norm without a backup handy , your mare is fine. She won't likely ever wear too short. If you start riding on rougher ground on a regular basis, her feet will adjust quickly, esp if they are truely that balanced already. If you aren't riding her as much or on softer ground, you will notice more to trim by the farrier. Usually when riding season is over, the first trim or two will take a little more hoof off, as it's used to the need to grow more, but by spring, just before you start riding, there's much less to trim because the hoof has adjusted to the idle lifestyle and is growing more slowly.
Sorry for the long answer!