Return evil with good. No matter what scowls or slander come your way, say nothing. Sometimes, a good gift can change things around completely.
I had something like this: I broke an engagement with a woman in the same denomination as me. She went on a raging campaign of slander. I said nothing.
This is what happened: everyone who knew something bad about her began to report it. She thought it was me saying those things... and started up even worse.
I still said nothing but kind things.
More and more bad truths came out about her. Finally, one of the leaders in the church, speaking at a conference mentioned the entire affair, without names. She came looking like a gold digger. I looked like a saintly victim. That ended the entire thing.
"Do unto others as you would have done unto you."
And remember, most times, the way people treat you is about them, not you. Consider that this unhappy person might really just need a friend, or someone to talk to in trust, or maybe just someone who acknowledges what is good about them.
More recently, a woman at a volunteer group did not like me. The Holy Spirit told me it was because she perceived that I only saw the part of her that was a barrier, a defensive wall.
The next time I saw her, I gave a big, "Hello, Susan!" (not her real name). She changed her attitude completely. She even offered to bring me some coffee!
Love conquers all.