Creamsicle Mollie acting odd.. Need help.

[FishForTanksNotBellies]

hey guys! I've got this beautiful Creamsicle Mollie that I purchased approximately two months back, she's acting odd and I'm quite worried about her. When we first got her, she was added to our 20gal hexagon tank along with two other Dalmatian Mollies, and two Dwarf Flame Gourami's. She began to exhibit some very aggressive behavior, especially during feeding time. We noticed that no matter how much we fed her, she never gained any weight! She began to become more aggressive, to the point where she was causing damage to our other fish. We moved her to a 20gal long tank by herself. For the first week, she was doing well. Swimming, coming to the front of the tank for food, and eating whenever we fed her. We noticed she still had not gained any weight, but her belly began to look sunken in. My question is, is it a possibility she has an internal parasite?

 

[FishForTanksNotBellies]

I put her in an Epsom salt bath for 20 minutes, now she's swimming around again.

 

[FishForTanksNotBellies]

Spoke with my LFS owner, who's been in the hobby for over 50 years. He said it's not likely that it's a parasite of any type. We had to move her, into the 20gal long because she was being highly aggressive. The tank was set up for about four days prior to her move, with filter pads from an already established tank along with plants. We checked our ppm, which ended up being 0.25ppm. (I know, not a good move on our part and this is our fault)