I'm sorry to hear that you're niece is going through this and I hope she ends up recovering from what she experiences.
In the past I messed with the Ouija Board as well and afterwards I felt strange presences near by me. It made me feel very uncomfortable, over time I chose to ignore it and pay no mind to it. Occasionally I still feel as if I'm being watched and whenever it happens I feel very frighten by this. Anytime I feel fearful I put the TV on and let something play through out the night so I don't hear anything going on in my bedroom. Just wanted to let you know that you're not alone. There's other people who experience the same thing as what you're niece is going through.
