Just after she was made regent, Blanche was informed by Louis IX that there was a plot by nobles to kidnap him. In response, Blanche got her knights and the communal militia of Paris and rode out to Louis. Once back in Paris, she paraded herself and Louis through the streets as a triumph against the nobles and sharing the victory with the people. After this, she faced many battles against the Southern France nobles and even an invasion from King Henry III of England. However, Blanche managed to hold onto her domains and even extended the French Royal family's power. She kept the peace by agreeing to sign the Treaty of Paris, in 1229. Blanche was so notorious that even Pope Gregory IX requested her help to help preserve Constantinople from the Greeks, but she declined to help. Blanche having control of the French army and being respected for having it shows how far her influence reached.
The difficulty of looking at Blanche’s power through legal documents is that they always had to be put through under King Louis IX’s legal authority. Most of the time Blanche and Louis are seen as having shared power, to the point that it is hard to see when Louis is the sole King. Documents show that Blanche was receiving letters about the governance of France that Louis did not know about, or even better, were written to Louis and had an end note to Blanche. After Louis came of age, in 1232, King Henry III of England still sent letters addressed to Blanche and Louis. This showed that even foreign powers respected and knew the influence Blanche still held, even after she stopped being regent.
When King Louis went to fight in the Crusades in 1248, and made Blanche sole regent again, King Henry III still sent letters but only to Blanche. By this point Blanche decided to use a seal, seals were only used by widows and men, and by Blanche having a seal she was showing off the authority that she could wield. She was proclaiming male privilege by using the seal and not hiding that power. Using a seal shows Blanche as independent, influential, and someone of political importance.
Blanche of Castile was a medieval Queen that held on to her influence and power and was respected by her contemporaries.