it appears the Norfolk Island Pine has been over watered. This is easy to do when the room is too dark for the plant to grow. Plants will go dormant if they do not have the correct conditions to grow. The right amount of light, warmth and water. If a plant is in a dark room it will go dormant and stop growing or slow down growth. These means it is unable to take up the water you give it. The water just sits in the pot, drowning the roots. Roots need oxygen to grow. They get this from air pockets in the soil. Many of the air pockets fill with water when you water a plant. Which is fine it the plant is actively growing. It will quickly use the water and the air pockets will return. There are also pockets of soil that still have air pockets, even after you water those have oxygen for your plants roots to use. If water sits in a pot for long periods of time those air pockets become completely saturated with water. If the plant is not growing, because the room is too dark the plants roots start to decay. Breaking down in the water. Like when you leave your hand in water too long, your skin starts to pucker. Your skin is drowning in water, so are the roots in your sisters plant.
You can move it to your room, as long as you do not put it in direct light. Put it in bright light, but not direct. The tree might start to grow again and take up some of the water. But, if the roots have completely decayed then there is no hope for your plant. All you can do is try. I would move the plant to your room. It appears to get more sunlight than your sisters. Just avoid getting direct sunlight.