Brave? She’s misguided. There is no reason she should not seek treatment. As the previous poster pointed out, this is a very treatable form of cancer with a very good treatment response history. In this case, I don’t trust the mother.
You didn't read the post that my response was to. It was a post about a 12 year old niece of the poster who has T-cell lymphoma and is committed to fighting for her life and undergoing chemotherapy etc. I agree with you that the 17 year old’s decision to not have a very likely curative therapy is misguided.
The problem seems to be the hospital itself being very jealous of its own recommendations to the point that they must be obeyed with no other inputs permitted. In this sort of thing second opinions are always warranted, even highly advisable, whiichever way the first opinion came down.