Platinum is what the color variety of you sick female (girl) gourami is called in the US. It's the same species as the blue gourami (they can tell, lol), so there might be aggression or breeding behaviors depending on genders & size. Sorry for the US slang terms, I'll try to do better.
Malachite Green is an old dye type of fish med. I actually like it for some things. It's good for external parasites like ich, some internal 1s too & has a mild antibacterial effect. It's a pretty safe treatment when you don't know what to try. I would start with half a dose in the morning & another half dose in the evening just to make sure your fish is OK with it. Then dose as the labal says after water changes. That species of gourami are fairly hardy with medication.
Did she eat any of the tubifex that you could tell? Be sure to remove any uneaten prepared food & dead worms. Did you have some cycled filter media to add to the hospital tanks filter? Without that you really will have to change about 50% tank water every day. Not too difficult in a small tank. Do you have a water test kit for ammonia, nitrite & nitrate at least? Test often if you can & tell us water numbers or range you see for each.
I'm not sure what the yellow is. Maybe from not eating for a week? Or digestive tract lining from not eating or from the betta water treatment (I don't know what that is, not something I've used. (a plant supplement?). A tiny bit of waste from food or a breakdown of the worms? Sorry, hopefully some else will offer ideas.
Is she still sitting on the bottom? Any more of the jerk/hiccup thing?
I am wishing you & your fish good luck! Keep doing water changes before you redose the malachite.
