hm, that's odd, right? Green crust. And it's been there so long. I'd guess it is hormones with your daughter causing "physiological nipple discharge". This can be various colors including green. MOST of the time, that nipple discharge will turn out to be normal. One thing that can cause it in a young girl is ezcema on the nipple. https://www.bci.org.au/breast-cancer-information/fact-sheets/nipple-discharge/ I'd have her see her doctor though. It doesn't hurt? Infection normally hurts or that would be another possibility. Let me know if there are any updates.