Is it right or wrong for a teenager to still wanna be in diapers?

So, my one "friend" is 17 years old, going into college soon, has a job, car, license, a great family, and awesome friends. But, she secretly wears diapers. When she is in her room or home by herself, she will wear them and actually go in them! She is definitely beyond toilet training, and she has no special needs or anything like that. She just wears them just for the heck of it. Is that normal for her to be 17, almost 18, and still wanting to wear diapers? Or is it just weird and she should stop doing that? I just want to know what my friend should do....