In the state of Massachusetts, is there any precedent to reverse a home sale once the deed has been registered?

Probably nothing at this point.  Other thatn selling below market value, for which the estate could recover money damages, you've written nothing to indicate that the representatiove exceeded her authority pr breached her duties to the estate.  Even if you could prove that she had done so, the estate could not rescind the sale unless it could prove that the buyer knew about the wrongdoing prior to the sale.  If the buyer was what is known as a bona fiide purchaser for value, the estate would be limited to money damages from the representative, and could not rescind the sale, even if the representative had engaged in wrongdling.