Can I refuse to give my (ex) friend her stuff back
Why are you being so mean to your ex friend and not giving her stuff back?
She was such a bad friend and always badmouthed me.
You have been wrongly insulted and belittled by an ex friend, but you can't keep her things. That would be stealing, she can hold you accountable in court for them. So it is best to avoid the hassle now and just hand them over to her.
Could you stop telling me to return her stuff? She can have her stuff.
I really do think this is the best way to go. Once she has her things back you shouldn't have to worry about her anymore. That should be a big relief.