A Guardian ad Litem must be an attorney who is tasked with investigating the case to determine the best interests of the child, and reporting that to the court, who makes the final determination for what is in the best interests of the child. For that reason, I would say that it would not be wise for a grandparent to fill that role, even if they were an attorney. As a grandparent, you do not have much in the way of custodial rights as compared toy the parent, especially in terms of a parent who is not unfit. That said, provisions could be made for visitation with you, but that would require the acquiescence of the ex. I would advise speaking to her about whether she would consider permitting you some visitation. Just know that she can say no, and the court would not be able to override her decision unless she is proven to be unfit in some way.