Her body will began to slowly shut down. She won’t die immediately but since her nutrient levels are decreasing, her heart rate might become slower, and weaker. Her body will hold onto her weight and fat since it doesn’t know when it’s gonna get the proper nutrients, so it’s fighting with itself to keep the body alive.
She will have brittle nails, weakened immune system, and constant head aches, chest pains, etc if she continues this unhealthy eating/dieting habits. And she might be ending up in cardiac arrest from not enough blood pumping and flowing to the heart.