Oh my...
wonton, I know your aquarium info says you are getting a bigger tank soon; but I need to reiterate that you need to do this as soon as you possibly can. In my honest opinion this is beyond what I would call overstocked. If your aquarium info is just out of date and you did indeed upgrade your tank, please update it so we can be of better help.
I see your nitrite is 10. is that correct? You will need to do a massive amount of water changes to not only bring that down, but also to keep it down with that many fish in such a small tank.
I'm honestly not sure what the "black things" are that are coming off, but the high nitrite is likely causing her scratching behavior.