Recovery Possession Of Agricultural Land

I'm from West Bengal and my father has joint property(agricultural) around 1 acres in Odisha. A village lady builds her temporary Hut near our land's front area(road site) around 2-3 decimal area calling PWD land. My father always told her for leave and she says "she will leave when we use that property" But now she is building her house with bricks and cement without knowing us also threatening us while stop them. She is there more than 12 years, now her house capturing our land around 5-6 decimal. what should we do now, we are facing a very low price to sell that land cause of this. How we will overcome this. Please suggest us.