You can keep them together with other larger South American cichlids, or even Silver arowana with no problem. I like to keep fish geographically consistent. They don't bother other fish if you keep them with other fish, but if you keep it solo for a while, it will become very territorial in regards to the tank space and not allow any new fish.
She had a dozen large giant danios in with her when she first went into the 240, though she made quick work of them. Within 3 days she was back to being a solo fish!
I like the idea of dithers though. Maybe I could track down a trio of 8"+ tinfoil/bala barbs in hopes of them being to large to eat outright. My only concern though with going that route would be that she'd just beat the crap out of them, and having severely stressed/injured fish in the tank is just inviting disease.