Difficult tenant changes mind after agreeing to leave

[Danielle Leo]

I have a difficult tenant in my most expensive unit. She pays rent on time every month, but since the day she moved in she has been complaining about the apartment’s condition, always asks for repairs and has been really rude and ungrateful towards me and my maintenance staff. After almost a year I’m quite fed up and asked her if she wants to move out when the lease terminated. She said more mean things about the apartment but signed the notice of lease termination. A week later, she asked me if it was still possible to renew since she couldn’t find a better apartment within budget (duh!) and I said no. Since then she became very angry and hostile, started sending me texts and emails saying nasty things and threatening to Sue me at the rental board. So much that I had to block her text but the emails came coming. She also threatens to block entry if I wanna take visitors to see the apartment. 
what’s the best action, fellow landlords? I realize that it’ll be quite difficult to rent the apartment while she’s living in it (she can block entry, or make it dirty and unappealing to the potential renter) which will hurt me financially. Part of me almost wanna give in and let her renew to avoid future confrontations. But I also don’t wanna send the wrong message that she can get what she wants by being a nasty person. Thank you for your advice.