Smileyface

When I play on a 1.12.2 forge minecraft server with Vic's modern warfare mod, I can do everything alright and its okay. But when my sister tries to join, when she looks at me in the game, she sees this weird black thing and when she presses f5, she sees like squid legs under her and this weird black thing that keeps going in and out of her vision. Also, when she goes into creative inventory, she instantly crashes. She gets java error "The game crashed whilst rendering item Error: java.lang.IllegalStateException: Not building! Exit Code: -1". I think it's because she is using fast render or something. There are no other mods installed and not texture packs, or shaders. I run the server on my computer, by the way. I am using forge version 14.23.5.2855. By the way, when I hold up a gun, she sees a black bow. When I hold other guns, she sees like a creeper attached to a skeleton in my hand or something. When I wear the games custom armor, she sees like the squid legs I mentioned or this transparent glitchy black frame around me and her. The mod works perfectly fine for me except for a little lag. I have done every bug fix I can find and no one seems to have the same problem as me. pls help.