As you mother and your father are US persons - there would be additional tax liability on their side.
Your mother should determine the basis of the property - that is mainly a purchase price.
Because half of the property was inherited by your mother in 2004 after your father died - her basis on that half is a fair market value of the property at that time.
Then - she will report the sale transaction on the schedule D part II - as long term capital gain.
Her capital gain would be $180,000 (selling price) - (basis) - and it is generally taxable up to 15% depending on her other taxable income.
As the donor - she may need to file a gift tax return if the gift amount is above $13,000 per person per year (for 2009) , but there would not be any gift tax unless the lifetime limit of $1,000,000 is reached.
as she transfered the money into the US - if the amount is more than $100,000, the person is required to file form 3120 - http://www.irs.gov/pub/irs-pdf/f3520.pdf (see instructions for details - http://www.irs.gov/pub/irs-pdf/i3520.pdf) to declare transfer from the foreign country. There is no tax associated with this form.
In additional - your bank might be required to report your transaction - so I would suggest to consult with the banker if they need any supporting documents so your transaction would not look suspicious.
Let me know if you need any help.