I think the easiest answer here is that the "How" in the last sentence is supposed to be "Now". Are you reading this from a PDF you downloaded that was scanned in with character recognition? because H and N can look very similar to a computer.

"How" is a complicated words, it include when, why, do what and the thing.

It is not really a question, it is an addition to the previous question in the sentence before. How the experts did it? How she is one of the experts? Visit my profile if you have more questions or want to improve Your English language skills: https://www.italki.com/ivranjes97

Thank everyone ：）

I can't easily explain this. I'd call it badly written. But let me try. I share your confusion. This - How she is one of the experts, writing books on flower arrangement. - is not really a question. The "how" appears to echo the one in the previous sentence, "She was curious about how ..." Then, the pronouns slip. The "she" who was curious is not the same "she" who is one of the experts. And there is no nearby referent for either of these. We have to assume that, somewhere earlier in the text, these two "she"s are explained. To my mind, the last sentence is really a sentence fragment in the form of an afterthought. It does not make sense on its own. The "how" is functioning as an interrogative adverb here, and it feels uncomfortable. To be clearly a question, it would want subject-verb inversion : "how did she become...?" But it does not do this, and is not a question. It is an expansion of what the first "she" is curious about. Taken together, I think this is probably most accurately considered a sentence fraagment. A quick fix would be to join the two sentences, as the meaning implies; "She was curious about how the experts did it, and how [ she = the other woman] had become one of the experts, writing books on flower arrangements. https://www.chompchomp.com/terms/fragment.htm This qualifies as, at best, ugly writing.