Canadian seller of U.S. property - tax withholding

[Michaela G.]

I'm supposed to close on a SFH in Atlanta on Friday, that is owned by a Canadian seller. She got screwed over by an American investor, who sold the house turn-key, but never finished rehab. She paid US$ 60,ooo.

I'm buying for US$ 60,000  - payable in a lumpsum within 12 months.  $ 100 down, no interest, no payment, owner financed $ 59,900.00

We're now getting the closing statement and the attorney says that seller has to pay $ 9,000 for federal income tax. According to the attorney this is based only on the selling price. But she doesn't have $ 9,000.00 and she's not getting payment until 2018 and she's not making any profit. 

Somehow that seems wrong to me. What if she had a mortgage for 59K? She wouldn't be able to sell, because she doesn't have the money for the tax withholding, even though she's not realizing any profit?

I've asked my accountant and he doesn't know exactly, without having to do more research. Has anyone else here ever dealt with this?