Niece keeps biting my son... Help!

My 10 month old niece keeps biting my 10 month old son. This time she got him on the face. My sister in law really doesn’t do anything when it happens but call her mean and a little devil. I don’t know what to do. We live with her for another 5 months. She has bit him 3 times in the last week. I cannot watch him like a hawk it’s hard. I turn my head and she’s trying to bit him. Agh. 😢 and my son bald his eyes out every time she does it.