Put a thick, clean piece of gauze over it and wrap the whole hoof with elastoplast. Then wrap some duct tape or other waterproof, durable tape over the to keep it dry and in place until the vet comes. Don't touch it any more than that. All you want to do is keep it clean and still - the more you touch an injury like that the worse you can make it.
If you have it available, you can give her a sachet of bute tonight, but otherwise I wouldn't give her any other pain relief until the vet arrives as he/she may want to assess exactly how lame she is on it.