Maybe, I don't know, but if she'd been that down in the 21st century, wouldn't that despondency have carried over when she was so out of place in the 19th? There's a scene where Thong-on thinks she's going to drown herself but she's just being stubborn about escaping back to her time and jumping into the lake is her latest nonsensical idea of how to do that.
The ending is confusing, at least in subtitles. But her decision to stay in the past makes a lot of sense once she finally stops fighting her situation and realises how much she'll lose if she goes back.
My read on the confusing parts is that Dr Pat knew of a book written by someone with her inexplicably missing friend's name and liked to think/intuited (Dr Pat being a reincarnation of Pad) that that was where her Bua had disappeared to. And apparently those imagined trips where Bua takes Thong-on to visit the 21st century were somehow more than imagined? Which makes no sense and isn't explained but how else could Dr Pat see them? Fun but very very strange, more happy vibes than logic.
Whatever that was supposed to be all about, if Bua had killed herself in the 21st century Dr Pat's reaction should have been very different. The writing on the end wasn't the best for clarity though so I can't offer that as definitive evidence :) Mostly I think the odd ending was just a short way of letting us know Bua did write her book, implying a happily ever after for the pair and cheerfully knitting the beginning and end together.
