Nether multiplayer lan issue

I was playing with my girlfriend in my world, with the lan opening, and when we go to the nether, passing by the portal, sometimes, i dont watch her, sometimes she doesnt watch me, like i was not in here. Also it pass when we return to overworld, when someone of us is "invisible" cant interact with the other(like attacking) but the other(who can watch the other player) can interact with the "blind".