Player duplication in LAN worlds

When my friend joined my server (to be exact lan server if it matters), on chat I saw duplicated info that she joined (screen). I thought that it's just minor bug with displaying info about joining the server. Few minutes later, when I was searching something in save files I saw that server had 3 playerdata files. I was confused because nobody except us known ip server. Later she saw that on players list there are two players with her nick, but one with steve skin. I tried to teleport to her and it teleported me to her clone(it stayed on spawn). I tried to kill it and it was kinda weird. It worked like a voodoo doll. Then she left and I kicked the clone.