Hi helpingfriend,
i've read a bit about this & it is quite normal 4 a young girl's cycle 2 b irregular in the first 3-4years of her starting her periods because it is something very new 4 a young body & therefore,its not unsual 2 have long periods or short ones or none at all.It is the same at menopause when a womans cycle is preparing to stop altogether because again,this is another change 4 the body.
Because ur friend is young & I presume since u didnt mention it,not sexually active,i wouldnt imagine she had any serious medical problems however,it doesnt seem normal that shes had a period 4 a month.
If she is worried about it (cos im sure it'd b awful 2 b bledding 4 that long) I suggest u try 2 encourage her 2 c her doctor just 2 make sure theres nothing wrong
best wishes
liz