My betta female ruby is really not improving. She's kept in epsom salt soln heated around 82 F . She's sitting on the bottom of her cup. I put her in the tiny cup because I needed to keep her heated and my hospital tanks have no heaters at the moment. So I know it seems mean and I don't like keeping fish in a cup but since she's been in the big tank heated she seems better.And I say that because she had a serious BM that I noticed when I changed her water this morning. but only a little bit. She swims up to get air then sinks back to the bottom. I honestly Don't see her improving I need to know what else can I do

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Edit: she came home from petsmart SUPER constipated with bad sbd. Only difference is last time she couldnt swim down deeper. Now it seems like she cant float. Also She is the only fish in her tank that has become sick. The platies are fine. Same with the cory cats. I'm really sad because I got her to recuperate some what, now she seems to be doing worse again. She sits on her fin its weird (pic to show)