the jar is in a 20g??? how big is the jar? and how big is ur rd?? it's not impossible to have jar and cichlids living together, but it's gotta be under the condition that the jar is the dominant one. because cichlids know to find shelter for em'selves (of course u'll have to provide 'em with caves, driftwoods, plants, wutever that works), they can hide when jar chases after 'em, but not the other way around. there's no place for jar to hide its elongated body.
and if u can put ur jar in a 20g, and by the coloration of it, ur jar's gotta be still pretty small. jar's personality take a 180 degree turn when it grow to a certain length...some say 11" mark, some say bigger, but da is true for almost every case. until that turn around in personality, jars are actually very mellow and sometimes timid even. there is just no chance for a jar to defend itself against an aggressive cichlid, let alone a rd!
as far as the recovery goes, i've seen much worse cases that have fully recovered. take my recently acquired festae for ex. the previous owner took it out from the bottom of the tank thinking it's for sure a goner. large areas of scales missing, skin torn, flesh showing. all fins have been chewed up to the end, the whole fish turned white and she was just lying on the gravels not moving wuz so ever. but after a few month of recovery, it's about 80% healed. now she's in my care, i'm just tryin to complete that 20% which is a tough job.
wow, i think i wrote too much, well, good luck with ur jar's recovery, they're tougher than u think, and let it out of that 20g asap please!