Legal Question in Elder Law in Massachusetts

Re: POA changing a will

Even if she has a DPOA, she cannot self-deal to the exclusion of others without being subject to challenge. An Attorney in Fact has a fiduciary duty to the Principal, in this case your mother, to carry out her wishes. If she changes your mother's Will or takes other actions which result in her own financial gain, you can challenge the Will and any similar actions.

If you believe that your sister is acting in a manner in consistent with your Mother's wishes and/or best interest you can petition the court for a conservator or at a minimum an accounting.

Having said all this, the legal expense in such actions is fairly expensive so I would suggest you be sure of your facts and the amounts involved should be significant.