It is not appropriate for the guardian to do this, but it is probably not illegal. The guardian must oversee your mother’s care and act in her best interest. The guardian is probably also required to file reports with the local probate court, but the specifics of such requirements depend on state law. Under state law, you may be entitled to notice of the reports. But the law likely does not require the guardian to specifically communicate with the next of kin. You would need to argue that it’s in your mother’s best interest.