Sounds like she either contracted a secondary infection during her ich infestation, or she had something systemic and that's what caused her to succumb to the ich.
If I had to point out a particular cause, I would say that your water change schedule in her hex tank was not enough to keep the ammonia down, and the ammonia caused her to get sick. Fish constantly excrete ammonia through their gills as waste, kind of like urine. In a closed system, there's no bacteria to break down this ammonia into less harmful nitrate and there's no plants to consume it which is what would occur in nature and in larger, planted and filtered tanks, so the ammonia just builds up.
The only way to control ammonia in small, unfiltered tanks is with frequent 100% water changes. In a two gallon container, you should be doing a 100% change every 3-4 days--during the change, you should wash out the container, gravel, and all decor with hot water to remove any food, waste, and residual ammonia. I also urge you to get a liquid test kit, like this one: http://www.fosterandsmithaquatics.co...54&pcatid=4454
so that you can tailor your water change schedule to your specific needs and so that you can be sure your schedule is effective at removing all the toxins in the water.
Sorry this happened, I know it's difficult to see them go like this. :( At least now you can do your best to prevent this from happening in the future.