It is not true that Thai people with dual nationality in general and — in the the context of this topic — in particular female Thai nationals who acquire another nationality by marriage under the laws of the country of which the husband is a national are legally required to claim only one nationality.
Aside from that, the excerpt of the post I am quoting is off topic but I am not removing the post because the rest of it is acceptable.
Anyone wishing to discuss an alleged legal requirement of the type mentioned above should feel free to start a new topic on this subject, citing the relative legal clause and giving a link to the text of the apposite law.