Hi emceesky and welcome to the forum. It looks like you've gotten a lot of good advice about housing girls together so I'll just back them up. Although pet stores will tell you differently, the truth is females should be housed in no less than a 10gal with no fewer than 4 girls. Otherwise there is aggression.
It looks like your blue girl may have sustained some internal damage. In addition, it looks like she had some bites or nips that developed saprolegnia, which is a fungus that often occurs at the site of open wounds. This is probably what caused her death.
For your two remaining girls, you definitely want to continue with 1 tsp of aquarium salt per gallon for no more than 14 days at the absolute max (10 days is preferable). If you can, get a product called Kordon Fish Protector OR API Stress Coat. Both of these really help with the healing process. Nipped and torn fins WILL grow back but it's really important you keep the water as clean as possible during this time to limit the chances of infection. Since they're in small containers right now, try to change 100% of the water once a day for a week.
Once you get a suitable tank, I highly recommend you come back to the forum and post a thread about starting a sorority. That way, a lot of people will be able to walk you through the process of putting your females together.
Also, try to keep the water warm, around 78-80 F. They will heal faster and better in water that is more to their natural habitat.