You do not need to submit any documents to prove her wages when you submit your tax return. Convert her income in US dollars and report on your joint tax return. However, you do need to prepare to show any paperwork which proves her foreign wages if you are contacted by IRS for any audits or correspondence.
On your Form 1040 joint tax return, if your spouse pays taxes to both foreign and US governments on the same amount of the income, she is entitled to claim a foreign tax credit on Form 1116. Please see Foreign Tax Credit
As far as filing either Married Filing Jointly or Married Filing Separately, to see the differences between the two, please see attached information.
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