Landlord causing my wife trouble, please need advice

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My wife has been renting a 2 bedroom home with a month to month lease for 5 months. She has been a perfect tenant, she's clean and takes good care of the home. She has never been late on a payment, never has done damage, nothing. Well, now this landlord wants to kick her and our two children out, so she can rent to someone she knows. Sounds very illegal so far, like discrimination or something, along with the mental stress she is causing my wife. She wants to rent to this person she knows, and it would be for a 6 month lease (instead of month to month (which the landlord agreed too) and the rent would be 50 dollars more a month. My wife said she would go ahead and sign a 6 month lease and pay the 50 dollars more a month (does she even have too?). So this lady landlord who my wife says has a bad attitude says no, she wants her to leave so she can rent to her friend. So it's kick a woman with two children out on the street just because she wants to. It sounds like this woman landlord is not following the law. Can someone tell me what we should do? What this woman landlord is doing cannot be legal. I almost feel like going to my wifes house and changing the locks, then calling this woman and tell her she blew it and good luck getting my wife out now. But instead I thought I would find out from someone who knows what we should do about this nightmare. My wife can't find another house right now and is scared to death and she has done nothing wrong, this woman just wants to rent to a friend and get a longer lease and 50 bucks more a month. What can my wife do to protect her home? Also, last month was the first month my wife didn't get anything from this woman showing she paid her rent. Each month before that when my wife paid the landlord gave her a new lease for that month, but not last month. So what should we do? thanks everyone