this happened to one of my creams, he was nice as could be but then one day decided to be very nippy. good thing for me he was under a year old and it didnt freak me out. the absolute most important thing when a snake starts biting is to do exactly the same you would with any other snake. give it regular attention (handling sessions aside from feedings) and be careful and gentle. dont pose a threat, and do NOT pull your hand away in fear. if you take it out, and it bites you, and you put it back your kinda training it to think thats what will happen every time it bites. you have to understand snakes dont like to be held, but with trust they begin to tolerate us. -- i know some will argue "my snake loves when i hold it, blah blah, it always comes to me, blah blah," but really, how can you know? maybe some do but its not of their nature. they are wild animals.
all in all, id tell you friend to make sure she keeps holding it, maybe even hold it more than any other of her snakes. it should come around as long as its not further neglected.