I had to deal with this one lady my age who was/is friends with a girl who used to bully me (I caught up with her and the bully is so far nice, it's been four years so it's possible, even likely, she changed). She was even worse than the bully, she constantly acted like she was going to attack me, screamed my name like she was my archnemesis in a story, and after sending threats to me, calling me names, and telling me to die, she made several other accounts with different names like "Kaitlyn", "Josephine", etc. all friending me and liking my posts. I knew it was her from the mannerisms, being friends with all the lady's friends, and one other thing: Kaitlyn was her username but her display name was kept as her real name.
She didn't do anything harmful but she tried to see who I was friends with, what places I went, what I posted, etc. She never answered my messages, though, she'd just look at what I posted and who was my friend.
frankly, the behavior is that of someone not quite right mentally.