I think it would be like most anyone else. You think to yourself (or someone tells you), "I (you) should write a book about [whatever topic]" and that's about as far as that project gets. Even professional writers and teachers/professors have difficulty actually starting to write a whole book, IMO.
If she had something that she felt was important to communicate, or if she truly enjoyed writing, I would expect to find lengthy posts by her on FB or a blog. I have never seen her FB account. Did she write much on there?
Did she take any community college classes in writing or literature? Even if she was not pursuing a degree, I would expect her to do at least that much if she really enjoyed writing or wanted to write a book.
At 19, I would have said, "Ha-ha-ha, no story here," but that's just me and there was no internet and self-publishing was truly a vanity pursuit.
JMO
eta - What would she write about that anyone would pay for?