sorry this doesn't sound good. When is she due to whelp (is this the right word with rays?)? With the bloody discharge I worry most about her pregnancy that she maybe having a dystocia meaning she can't pass the pups, there was an uterine torsion or that a pup (s) have died and now she has an uterine infection. There are obviously a lot of causes of bloat but with the discharge I would definitely guess pup related. Unless the bloody discharge from the cloaca appears to bloody stool then it is is most likely uterine. I would definitely get her into her own tank. The salts won't hurt but think her best shot is with antibiotics. If you have a vet by you that can give you injectable that is your best shot.
Dystocias have been reported i these guys. Another thing to consider (which is not low stress but might be life saving) is to take her out and do a cloacal exam (with gloved finger of course) and see if there is a blockage you can palpate and remove. This is best done under sedation if you have that option. I hate to say if you loose her you should definitely try to do a necropsy at home with pictures to determine what happened.
If you can't get injectable, you could consider oxytratracycline or kanamycin. both will affect your filter
