Elena Asenina was the wife of Byzantine Emperor Theodore II Laskaris in the mid 13th century. Her husband was a great reformist who attempted to break the power of the big aristocracy, but his early death doomed his dynasty and his reforms. IOTL he was succeeded by his young son John IV, with his best friend/foster brother George Mouzalon as regent. Michael VIII Palaiologos, Theodore's arch-enemy, overthrew him almost immediately and blinded John IV after the reconquest of Constantinople.
Supposing that Elena lives and Theodore II still dies on schedule (although his wife's death probably worsened his epilepsy in OTL), how does the transfer of power work out? Elena would now be the regent for John IV, with George Mouzalon as her chief minister if she intends to continue on her husband's path. Does Michael Palaiologos still attempt to overthrow the Empress, rather than a massively unpopular and lowborn chief minister who no longer had a patron? If he does try to coup her out of power, will he marry her forcibly as other usurpers did before? What would it mean for John IV? A situation similar to Romanos I Lekapenos and Constantine VII, or is he still blinded and monastically exiled? How would the Nicaean/Byzantine society react to Michael VIII blinding his son-in-law, rather than merely the boy junior monarch who had a perceived tyrant for a father? How does Bulgaria react?
Finally, if Elena and George Mouzalon manage to avoid a coup by the traditional aristocracy, how does the regency and John IV's reign play out? What does the absence of a Palaiologos dynasty mean to the Byzantine Empire? When is Constantinople reconquered? Do the Sicilian Vespers happen as they did, without Michael VIII's interference? How does the Byzantine society look like without the Church unionism debate? Will the Laskarids place greater emphasis on holding Anatolia? Successfully?
Supposing that Elena lives and Theodore II still dies on schedule (although his wife's death probably worsened his epilepsy in OTL), how does the transfer of power work out? Elena would now be the regent for John IV, with George Mouzalon as her chief minister if she intends to continue on her husband's path. Does Michael Palaiologos still attempt to overthrow the Empress, rather than a massively unpopular and lowborn chief minister who no longer had a patron? If he does try to coup her out of power, will he marry her forcibly as other usurpers did before? What would it mean for John IV? A situation similar to Romanos I Lekapenos and Constantine VII, or is he still blinded and monastically exiled? How would the Nicaean/Byzantine society react to Michael VIII blinding his son-in-law, rather than merely the boy junior monarch who had a perceived tyrant for a father? How does Bulgaria react?
Finally, if Elena and George Mouzalon manage to avoid a coup by the traditional aristocracy, how does the regency and John IV's reign play out? What does the absence of a Palaiologos dynasty mean to the Byzantine Empire? When is Constantinople reconquered? Do the Sicilian Vespers happen as they did, without Michael VIII's interference? How does the Byzantine society look like without the Church unionism debate? Will the Laskarids place greater emphasis on holding Anatolia? Successfully?