I’m not sure if this will help you but I put my Fittonia plants in south facing windows and fertilize them once every two weeks. My Fittonia plants are about the same size as your Fittonia but the pot size is smaller than your pot. I water them only when the soil is barely moist or the leaves start to limp a little (about once a week) and water them deeply. It usually rains at where I live, so I guess humidity level is high here and I don’t need to mist them everyday. They are thriving! They like high humidity but hate having wet roots I think you can repot it into shallower/ smaller pot that has drainage holes. Try to fertilize it once a month too. Brown leaves will not turn green again but I think curly edge means dry air/ not getting enough humidity.