Without knowing exactly whats wrong, its better to not randomly medicate your fish. It can do more harm than good. That beign said, is this fish in an isolated hospital tank, and if it is the one you used earlier today, has it been steralized? You don't want your new rescue catching what Flash died from.
For the time being, I would add aquarium salt and stress coat to his water. She could also be just stressed from bad water conditions, then the move to your house. I would put her in a dark room that is quiet so she can rest. You can try to offer her a little food, my betta that I rescued was just very weak, but make sure it is small amounts at first, incase she doesn't eat.
Don't play with the temperature one way or the other from where you have it, becasue some disease thrive in warmer water, some thrive in colder water.
Make sure to watch your fish very carefully, and
THIS THREAD has a list of what different symptoms may mean.
EDIT: I'm not very familiar with mollies, so make sure they can have salt before adding it.