Christep.
You do not have to pay US taxes on income outside the United states if you don't live in the united states and are a US citizen. Furthermore if you work outside the USA and don't spend more than 30 days or so in the USA as a US citizen (like many expats do) you can bring 70,000 dollars into the USA completely tax free every year and any money you keep outside the USA is untouched....
But the long and the short of it is, if she holds dual citizenship but doesn't live the USA she will never be taxed by uncle sam.
Just more crap from the bash the USA crowd...
Cheers
Wino