The first question to ask is whether the widow (if she were competent) could make the changes herself. Typically trusts become irrevocable upon the grantor's death. The successor trustee (which she probably is) can usually make decisions on the administration of the trust but only to the extent provided by the trust document. If the person granting the power of attorney can't act, neither can the attorney in fact.
The second question is how a power of attorney was established for an incompetent person. It would have had to been done before she lost competency and specifically provided for such durability.
