I need some advice pls. i sold a piece of land to a close friend of mine. she has no enough cash to pay the?

full amount. so she told me she will issue four checks in addition to small cash she will give me. she gave me a cash of about 5.000. now we did not register to her name yet, but instead i gave her authorization ( thru the court) meaning she can sell it or do anything without my agreement. now the problem is, she doesnt want to issue the four checks we agreed before, now what i need to know, is there a way i could do to stop my authorization to her. she is my friend and i trusted her too much, not knowing that she could cheat me. please i really need advice.