What temperature is the water? How often do you clean it? Those "baby bettas" are actually just the runts and weaklings of the spawn from the farm they get them from - they are stunted for the purpose to sell as "babies". A good number of them don't survive.. best bet in caring for it is to make sure the temp is 80-84F, fed 3x a day foods such as NLS Grow formula, and live foods and water changed a few times a week.
Outside of that, not much else you can do - salt is fine to use, would use no more than 1tsp per gallon.
Hope she gets better for you!
Last edited by Myates; 11-01-2013 at 04:03 PM.