Depending on the country and time period, women and children had absolutely no rights without a male relative as their guardian. So when the father died before his son was of age, everything would go to his next adult male relative (his brother). So why should the brother be willing to give the inheritance back to Florenci when he becomes an adult?
To add to this many woman where ridiculed in high society if they didn’t conform to its norms and expectations. If your engagement had been broken off, you where seen as damaged goods. Because there must have been a reason why the marriage would be called off. It was unusual for the female side to call it because they where often ridiculed and punished, so usually the grooms side called it off. They wouldn’t receive as much ridicule. And it was easier to find a new match for the men than for the woman. Even if one was of higher standing high scociety would still gossip and ridicule you for any fault. A real life example would be empress Sisi, she was a common target for high society ridicule at the time even though she was the empress.
there's so many things that makes no sense
1. she's froma ducal family, just under an archduke, she's in no way a low rank noble so how can ppl openly criticize her like that?
2. tho they have to protect themselves from her uncle, they have land and a title. sure she locked it and gave it to the king until her brother is older, but they have a high enough status to find a legitimate guardian and/or work in the palace as a lady-in-waiting
3. how can her uncle be so influencial that he could just steal the title with no signature from her