I'm sorry she's having problems. Since she's 3-4 years old, you must be doing something right! That's a long life, and it's possible that she's starting to feel her age a little. (For example, missing the food, etc.)
I would stop using the aquarium salt. It contains sodium, which can contribute to bloating and fluid retention, which in turn can cause buoyancy issues. Plus, the sodium causes stress on the kidneys.
Since she's having buoyancy issues, I would try using Epsom salt instead. Look for 100% magnesium sulfate. (No dyes, perfumes or additives.) It has a laxative effect, and should help eliminate bloating and fluid retention. Start by adding 0.5 teaspoons per gallon. (This would be just 0.25 teaspoons in your half-gallon tank.) Dissolve the salt completely in some conditioned water, and add it to her tank slowly. She can remain in this for up to two weeks, if needed. If the buoyancy issues continue, you can increase the Epsom salt to 1 teaspoon per gallon. (0.5 teaspoons in your half gal tank.)
Why do you want to switch her food? If she's been doing well on the micro pellets, I would just keep feeding her those. She may not like the new food as much, so she's not overly interested in eating it.
If she keeps missing her food, contact AyalaCookiejar. She has a blind betta, so she may have tips for helping your girl track her food better.
Last edited by LittleBlueFishlets; 04-13-2013 at 11:53 PM.