Cichlid feeding aggression?

I recently added a Jewel cichlid in with my Jack Dempsey in my 75g tank and despite the odd behaviours of the jewel (hiding by the heater, eating bubbles from the bubble wand and then spitting them out all day long) everything has been normal but the jewel hasn't been eating. My JD eats like a pig and would eat for hours if I fed her that much. I finally got my jewel to eat but as soon as the JD saw her eating her food she went ballistic chasing the jewel till she went a hid in a cave too small for the JD. When the jewel was eating was the first time she was acting like a normal fish. After feeding jewel went back to hiding and JD left her alone. How can I fix this? If my jewel doesn't eat more soon she's probably going to die soon.