While her role is regarded as crucial in repulsing the foreign forces out of Poland-Lithuania during the Swedish Deluge (1655–1660), she became increasingly unpopular for her absolutist policies and her intention of nominating her niece's husband, Henri Jules, the future Prince of Condé, the heir apparent to the Polish-Lithuanian throne.

After Marie Louise's death, John Casimir hesitatingly renounced the crown, and the Commonwealth government officially curtailed the prerogatives of the royal consort.

[1] Marie Louise was supposed to marry Gaston, Duke of Orléans in 1627, but King Louis XIII of France strongly opposed the marriage and subsequently imprisoned her in the Château de Vincennes and later in a small convent.

Marie Louise believed that she was more able to control John Casimir rather than his deceased brother Władysław, who was described as extremely stubborn, self-centered and overwhelmingly supporting the nobility.

Intelligent, tenacious and with a strong personality, she not only supported John Casimir many times but also guided him throughout the entire political and several military campaigns.

That was noticed by a Brandenburgian diplomat, Hoverberk, who stated in his diaries that "by incessant insistence, molestation, complaints and other tricks she controlled the poor king and therefore the entire ill-fated country itself."

Marie Louise opposed Commonwealth's policy of religious toleration, believed that Poland was a "place of shelter for heretics" and wanted them burnt at the stake.

She brought many noble ladies to the Polish-Lithuanian court from France who would be obliged to marry voivodes, princes and wealthy landowners and eventually serve as a defensive shield if the higher classes decided to rebel against the government, one of the most well-known examples being her relative and favourite Klara Izabella Pacowa.

Reportedly she risked her life on the front lines and after the defeat, was forced to leave the capital, she did not lose her faith in victory and went to Silesia, where she directed the army to fight against the invaders.

[4] During the invasion, the queen reached the peak of her popularity, but that quickly passed after the presentation of the draft reform; the strengthening of royal power and election vivente rege (Latin meaning "for the life of the king").

At the same time, she was determined for her niece, Anne Henriette of Bavaria, whose husband was to be Henri Jules, Prince of Condé, to be the wife of the next elected King of Poland and Grand Duke of Lithuania.

This enraged the wealthier classes and the nobles, who accused her of meddling the Commonwealth into French politics that were hostile towards England, Sweden and allied Austria and Russia.

John II Casimir and Marie Louise were forced to give up their plans of reform and were obliged to declare amnesty for the rebels, while Lubomirski signed a letter of apology.

The great effort put into the stabilization of the economy and the subsequent political disaster rapidly affected the health of the queen, who was suffering from fever, severe weight loss, constant coughing and a permanently bleeding nose.

She was the patron of the next king and grand duke, John III Sobieski, who would follow the example of trying to reform the Commonwealth's legal system, also without major success.

Together with Bona Sforza, she was without a doubt the most energetic and the most important Polish queen and Lithuanian grand duchess of the modern age and played an instrumental role in repulsing the Swedish armies during the Deluge,[9][self-published source] but it was her stubborn nature and ambitious plans for reform that led to her demise.