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First she would have the burden of proving that you owe her the money and she will need to show the tax return in Family Court.
You can order a tax transcript from the IRS, at their website as well.
Requesting transcripts (individuals):
You have three easy and convenient options for getting copies of your federal tax return information--tax return transcripts and tax account transcripts--by phone, by mail, or online.
Our new online ordering method, Order A Transcript, is available and makes ordering simple.
You may also request transcripts by calling 1-800-908-9946, or order by mail using IRS Form 4506T (Request for Transcript of Tax Return).
We do not charge a fee for transcripts. Allow five to ten days for delivery if you order online or by phone.
A tax return transcript shows most line items from your tax return (Form 1040, 1040A or 1040EZ) as it was originally filed, including any accompanying forms and schedules. It does not reflect any changes you, your representative or the IRS made after the return was filed. In many cases, a return transcript will meet the requirements of lending institutions such as those offering mortgages and for applying for student loans.
A tax account transcript shows any later adjustments either you or the IRS made after the tax return was filed. This transcript shows basic data, including marital status, type of return filed, adjusted gross income and taxable income.
This is from the IRS site