having studied business finance at Mahidol, I do have a fair bit of knowledge about Thai accountancy.
You can bring any amount of savings into the country tax free.
What they are seeking to tax is income derived os while you are resident of Thailand. And even then, if you show you have already been taxed, you aren't taxed again.
Do your research and don't assume everyone is as stupid as you
She already knows if she upgrades her passport and citizenship to say that of a European, American or Australian they can not only travel easier, but get pensions etc