I'm sorry for your little girl.. without a picture it will be hard to say for sure what is wrong. Usually it's gold to rust coloration you see when shining a light on it.. but it could very well be what she has. I would try to get some pictures of her now before treating her just yet..
You would treat it as you would Ich-
You can treat Ick either conservatively or with medication. Ick is a parasite. Because ick is contagious, it is preferable to treat the whole tank when one fish is found to have it. Ick is temperature sensitive: Leave your betta in the community tank and raise temperature to 85 F. Then you can choose to treat with salt or medication. Conservative: Add 1 tsp/gal Aquarium Salt 3 times, 12 hours apart so that you end up with 3 times the normal concentration. Perform daily 100% water changes to remove fallen parasites before they can reproduce. Replace the water with the right amount of salt. Do not continue this treatment for more than 14 days. If it fails or you do not want to use salt, treat with Jungle’s Parasite Clear, API Super Ick Cure, or Kordon Rid Ich Plus. If your betta lives in a jar/bowl, then it can be difficult to heat the water. There are heaters for smaller containers, but you can also float the quarantine container in a larger heated tank during treatment. Do a full water change every day and add an appropriate amount of medication to the water.
A few tips though on other aspects:
Feeding a lot of pellets in one meal, one meal a day is a dangerous habit to be in. It could easily bloat her and cause her to have SBD.. it's best to feed smaller meals, multiple times a day. A good way of doing it is 2-3 pellets for breakfast, and 2-3 pellets for dinner- feeding when you eat. Helps her digestion be able to keep up and it won't cause her to bloat as pellets do expand some while in the stomach, and their stomachs are the approx size of their eyes.
"dose of bettafix, aquarium salt, expired maracide" Is a very dangerous combination. AQ salt should never be used with other medication at the same time- Bettafix is highly not recommended as it has an ingredient (a tree oil) that has potential for harming their labyrinth organ. It's a watered down Melafix which is very bad for bettas... and you usually don't want to use expired medicine. For humans, sometimes it just means the medication isn't as strong, but unsure about these types of medications. It's always wise to never use expired medicine for us or animals.
You may want to up your water change since it is less then a gallon.. normally 1-4 gallons you do 1 50% and 1 100% water change per week.. for 3/4 of a gallon, I would do that plus one more 50%.. so would be 2 50% and 1 100% per week to make sure the water is clean and safe.