MY SISTER IS TRYING TO SELL MY MOMS HOUSE AND WE ARE BOTH ON THE POWER OF ATTORNEY, CAN SHE DO THIS?

I am assuming that your mother is alive.  If that is not the case, then my answers would certainly be different.  Your sister's ability to transact business regarding the property are depending on the scope of powers given to her by your mother as set forth in the power of attorney document.  You should review that first if you have it. Agents (or attorneys in fact, which is what your sister is) have a strong legal duty to act in the best interest of the Principal (your mother).  They are prohibited from engaging in "self-dealing".  If your sister, as agent for your mother, signed a deed transferring your mother's house to herself, that would be a transaction that needs further scrutiny.  Does your mother have congitive deficits or other conditions that impair her ability to manage her own financial affairs?  If not, did you mother consent to the transfer?   Assuming the worst case scenario that your mother is incapable of managing her affairs and that your sister transferred the house to herself without your mother's knowledge and/or consent, then yes you can take action to call your sister to account for her actions.  If she cannot properly account for them, then she can be removed as your mother's agent and be forced to return any property or money that she converted from your mother.  Those would be proceedings that you would initiate in the Orphans Court of the county in which your mother resides.