Truthfully, I would go ahead and have her shod. A good farrier will not do any sort of damage at all and the shoes will keep her from wearing her feet completely down. Plus, they will provide some protection against stone bruises from smaller stones.
The thing about a job like that, if she comes up lame, you're just absolutely stuck. If there are a ton of big rocks that you'll be going at pretty high speeds over, I would be tempted to put some sort of pad on her as well, just to keep any rocks from bruising her sole where it wasn't protected by the shoe.
Do you have a backup horse ready in case something does happen and she pulls lame for whatever reason?