Sold an iphone 5s she wants money back?

I don't know anything about apples
brother gave me unused for work i've done. Posted on craigslist and sold it. Lady was talking scams repeatedly during purchase, 2 days later she calls saying everything was fine for a few hours, then she had Difficulty plugging into computer properly, Then problems started "?" i don't know if that connection attempt screwed up phone or what she has done to the phone since taking it. My brother says she was so avid speaking of scams, maybe she is trying to scam you by giving you a broken i5s because they All look the same. Now lady is threatening legal saying she has my license plate number and vehicle description.
i don't know anything about apples. What do i do?

The legal phrase is "caveat emptor" - buyer beware. She bought it as seen - now she wants to dump a broken phone on to you and she keeps the one you sold her. All she has to do it switch the SIM's.
She says it "everything was fine for a few hours" - what is the chance of it breaking just then?
She is attempting fraud on you. Tell her she is wellcome to start proceedings and you will counterclaim for harassment, attempted fraud and costs.