Tax Implications of Quit Claim Deed

hello. my mother in law, who lives in iowa, presumably inherited 60 acres of farmland in oklahoma many decades ago and has no paperwork to document the transaction. she recently "sold" this inheritance to a relative who also owns oklahoma land by similar inheritance many years ago by way of a quit claim deed and received a check from the relative for $18,000. since my mother in law has only sold her interest in the property and not the property itself, is she responsible at this point in time (year 2010) to report long term cap gains to irs, calculating basis, and paying 15% tax on the "profit"?

thanks for helping to clarify. i have not been able to document what she actually owned or "sold."

- son in law in virginia