My friend's brother used to restore old motorcycle engines in their shed. The whole house would shake, it was brutal. They finally made a deal for specific "loud hours" on weekend afternoons. He got his fix, and they got guaranteed quiet the rest of the time. Maybe a set schedule like that could work? She gets to tumble her rocks, you get some peace, and you can still check out the cool results after.
My old roommate had a pottery wheel in the garage. We set up a strict 2-4pm window on Saturdays for the noise. It saved our sanity and the friendship, honestly.