You forget the fact that the snow queen didn't use her full powers against eric. She wasn't in a rage as she was when she noticed Emmett has escaped. As I said before she only wanted her intruders to leave. Her desire for Emmett has given her a lot of energy and that's why she is so strong. You could always have changed it by making one of the guys taking her spear. Without it she is less powerful. My plot would have been Emmett and jake would not have taken the sleigh and they would have faced her again but this time a bit more aware of her powers