over stock IMO, also redtail sharks are very aggressive when reaching maturity. they can be kept with other fish at a young age, but usually the buyers aren't informed that they will attack bottom dwelling fish. they create a territory etc etc. usually are kept with cichlids.
if she is being attacked then i would say that the shark is the one at fault. put her in the 10 gallon, with a bubblier, lots of hiding spaces and a heater. you don't need to filter it as you can do water changes, which will be very important to keep the water quality up because she isn't doing so good. keep the cave that she is in to the 10 gallon so she has something familiar.
treat with either metaflex and pimaflex or methylene blue. now with the methylene i would go with that first, it'll kill any live plants so make sure you don't put that in if you have live plants... so the 10 gallon. also with the blue you can't really over dose it... first do a 50% water change so that it'll be 50% of old aquarium water and 50% new (having a bubblier and heater is crucial), then add the drops. then the next day add another 10 drops.
now the german rams and kribensis when older might have some issues with territory. just a thought for the future.