I solved the problem, something was very wrong with the river rocks I bought her. I cleaned them so carefully, but it's the only thing I can put it down to.
Anyway .... I checked on her the other morning, and she was trying to leap out of her tank, so I checked on her again a few hours later, and she was sitting very still, and she appeared to have lots of fungus. I honestly thought she was dead for a few minutes, and felt very guilty, because I felt like she was trying to tell me something by trying to leap out of her tank (I didn't think too much of it, because she always does it when I take her out and put her back in)
So I scooped her out straight away, scrubbed the tank from top to bottom, and got rid of the stupid rocks. Within 6 hours, her skin had totally cleared up of the fungus looking stuff, and I could see some shedding skin around her gills and mouth, and a few random spots on her body. She was visibly stressed, and spent a lot of time 'sleeping' (well, I assume she was sleeping, she was very still for hours and hours). I checked on her last at 11pm before bed, and by 10am the next morning, her skin was looking loads better, and she appeared to be interacting with me like she normally does, eg - swimming over to me, and moving about. It's 4pm now, and I can only see a tiny bit of shedding skin around her mouth and gills, she's still flapping her gills a little bit, but her tail is uncurled now, and she seems to be acting a lot more normally.
I'm keeping a very close eye on water quality, and when I check this morning, there was virtually no ammonia and nitrite, and the nitrate reading was incredibly low. The temperature is around 16 degrees, and I'm trying to keep it cool. Is there anything else I should do? Is it ok to feed her, or should I wait until she's acting like she wants food like she normally does? Sorry for all the questions, the health and welfare of my pets is very important to me, and I feel like I screwed up for not realising there was something wrong with the river rocks :sad: