Thanks! Do you have anywhere you could possibly take a sample of your water to be tested? Investing in a decent liquid test kit would be a smart investment in order to catch problems before it can have affects on a fish's health. I am glad to hear that you have stepped up your water changes!
In respect to your fish, the fact that she has perked up after a big water change makes me suspicious that something was amiss with the water. The first place to start when fish health is in question is with water quality and water changes are a great start to helping remedy problems.
Let see how she feels over the next 12hrs and if there are any changes in her behavior or appearance. Don't hesitate to do another water change tomorrow either! If things do not improve or appear less positive, then moving her to a separate tank and treating her may be necessary.
Is the red area only on the area visible in the picture or are there other areas? The single area actually appears to be a scrape but if there are multiple areas, this is important to know. You also mentioned tiny red dots- are these everywhere? Does she have red veining in her fins and/or tail? These symptoms can be the direct result of a water quality issue but they can also indicate an internal infection. An internal infection typically presents with obvious symptoms- listless behavior, lack of appetite, possible bloating, etc. Keep a close eye on her and let us know how she is doing!
