But we still don't know if the trust is part of the deceased's estate or not. If not, where does the child support come from? Even if the law and/or the trust allows court to invade the trust principal, but it does not necessarily mean that the court would indeed do it, especially when the trust does make the child a beneficiary and allow him to stay there for free.
As I said earlier, this issue is very complicated. If she thinks it is worth the money and efforts, the best bet would be a competent attorney. One thing for sure, it is not going to be cheap. Given what is at stake, I probably would not do it.