It could be many reasons why this is happening. first off, Is your girlfriend still covered by warranty? If so, I would just contact apple. Because, anything we might recommend could potentially void your warranty. Otherwise, I would check the bottom of the laptop. Look for any signs of battery problems. Maybe some protruding or warm to the touch. Your battery could be swollen and or broken. I am not very well versed when it comes to apple products. So I would recommend waiting to see what everyone else says.