How did Princess Argyro lose her breast?

"Could there be connection to the legend that had the Amazons burn or cut their right breasts?"

In fact, it seems that that is exactly the reason for her title. An article on Proto Thema, a Greek newspaper, writes:

[Google Translate] "The traditions for Monovyza, probably have a historical basis. They may refer to the destruction of Phenicia by the Teutonic queen of the Illyrians, in 231 BC. According to tradition, her son Ίoulos was killed in a battle and his mother, in order to take revenge, decided to destroy Epirus. However, according to Appian (Illyrian, 7), Teuta did not have her own child. Her husband, Agronas, had a son, Pinnis, from a previous marriage...The people of Epirus named the princess "Monovyza", either insultingly or to declare her warlike nature. The word Monobyza, like the Latin Unimammia, means Amazon, because later writers mispronounced the word from the deprivative alpha and the masculine = breast. According to this paretymology, the myth was created that the Amazons cut their right breast so as not to prevent them from javelin throwing and archery. Caesar Dapontes in his work "Mirror of Women" (1766), calls the Amazons "Monovyzousa"."

In other words, both Argyro and Queen Teuta who may have been the basis for Argyro's legendary aspect, were called by a term that was used to refer to the Amazons, a term that meant 'single-breast' but was misinterpreted later on to literally mean that they had only one breast.

The idea was, as was put here:

[Google Translate] "In almost every region there is a different version of the myth. However, the core idea remains the same in all of them: Monovyza is a very strong woman with supernatural power."