For an advanced cross beak, I would not trim the beak. Trimming is for over-growth, not cross-beaking. The cross beak will probably continue to get worse until the bird is no longer able to take enough nutrition to support life. Provide a deep tray of food so the bird can place the beak deeper and maybe get more food. Unless you're willing to hand feed the baby for the next 5-7 years, you may want to consider euthanasia. I'm sorry you and you chick-child are going through this.