If it started as pastel, then it most likely has IMG traits somewhere.. From what I've read, it's random, non genetic(in the common sense of the term (rescessive/co-dom/dom..) and will eventually return to her normal pastel coloration.. But I could also be wrong and over looking a key bit of info.. After all it's 5 AM here..
http://www.ralphdavisreptiles.com/co...all_python.asp