I would go back to the beginning. Is your DD on board with the grade skip? Do your have the full support of the school adminstration/teachers? In other words, make sure that it is a writing issue. If it is a writing issue, then you need to narrow down the source of the angst and assess the level of her writing. If she is already at a 6th grade level, I would not push it and make the situation worse. It may be that she resents having to work on it over the summer and/or with her parent.