Hi dancersmama and welcome to the forum. I'm sorry about your girl. It looks like she may have possible renal failure in one of her kidneys, judging by the location of the bulge. In this case, Melafix would not help your girl because the problem is internal and Melafix is only effective as an antiseptic for external wounds such as ulcers and missing scales.
First, I would increase the dosage of epsom salts to 2 tsps per gallon and it's okay to leave her in the epsom salt mixture round the clock.
If the kidney infection is being caused by a bacterial infection, which it probably is, then the only effective way to treat it is with a medication that absorbs well. This medication would be Seachem Kanaplex but it's unfortunately very hard to find and usually has to be ordered online. A second option to try would be metronidazole, which can be found in the medication API General Cure. Metronidazole is mainly for parasite use but in some cases it can be effective for internal bacterial infections. It's not the best choice but it will be the most effective because it absorbs well. No other antibiotic on the market will work, unfortunately.