No real hair loss issues for Bow, but she complains that her scalp is itchy. I reckon its definitely the water. That may well be compounded by the fact that we're in London and the air quality is much worse than where she lives in Thailand.
I agree with the comments regarding cosmetics. If you can reduce the amount of things that are different, that should improve things.
There are, of course, the more obvious cultural differences, these, and the fact that a Thai partner who has uprooted themselves (permanently, or semi-permanently) may well be feeling stresses that are more difficult to pin down, if you can have some familiar things like cosmetics and hair products then that will, I believe, make things easier.
Also, the first time I was in Thailand was quite a shock to my body. Food, water, sun, insects etc. As I've been there quite a few times now, these things have less of an impact now. It seems that my wife has reacted less to those differences on her second visit.
It may be that a lot of these reactions are symptomatic of underlying stresses related to the whole 'newness' of everything rather than any specific thing that can be isolated and countered directly.