Girolamo is killed, after more than a half dozen failed attempts, on April 14, 1488 by a conspiracy led by the Orsis, a noble family of Forlì.
The lord's palace is sacked, while Caterina and her children are made prisoners.
The fortress of Ravaldino, a central part of the defensive system of the city, refuses to surrender to the Orsis.
Caterina offers to attempt to persuade the castellan, Tommaso Feo, to submit.
The Orsis believe Caterina because she has left her children as hostages, but once inside she lets loose a barrage of vulgar threats and promises of vengeance against her former captors.
According to a legend, when they threatened to kill her children, Caterina, standing in the walls of the fortress exposed her genitals and said: "Fatelo, se volete: impiccateli pure davanti a me... qui ho quanto basta per farne altri!"
("Do it, if you want to: hang them even in front of me...here I have what's needed to make others!").
Shocked by this response, the Orsis don't dare to touch the Riario children.
With the assistance of her uncle Ludovico il Moro (very interested in securing some influence in the Romagna, to counter the influence of Venice), Caterina defeats her enemies and regains possession of her dominions.
On April 30, 1488, Caterina becomes regent for her eldest son Ottaviano, formally recognized by all the members of the Commune and the head of the magistrates as the new Lord of Forlì that day, but too young to exercise power directly.
Caterina's first act as Regent of Forlì is to avenge the death of her husband, according to the custom of the time.
She orders that all those involved in the Orsi conspiracy are to be imprisoned, along with the Pope's governor, Monsignor Savelli, all the pontifical generals, and the castellan of the fortress of Forlimpopoli, and also all women of the Orsis and other families who had assisted in the conspiracy.
Soldiers seek out all who had taken part in the conspiracy.
Houses owned by those imprisoned are razed while their valuables are distributed to the poor.
News comes on July 30 that Pope Innocent VIII has given Ottaviano Riario the official investiture of his state "until his line ended."
In the meantime, Forlì is visited by Cardinal Raffaele Riario, officially to protect the orphan children of his late cousin Girolamo but actually to oversee the government of Caterina.
The young Countess personally deals with all issues concerning the government of her city-state, both public and private.
To consolidate her power, she exchanges gifts with the lords of neighboring states and involves herself in marriage negotiations for her children.
She decreases taxes by reducing some and eliminating others, and sharply controls her realm's spending.
Caterina deals directly with the training of her militia in the use of weapons and horses.
It is her intention that her cities and towns be orderly and peaceful, and she expects her subjects to appreciate these efforts.
Two months after the death of Girolamo, a rumor is spread that Caterina is close to marrying Antonio Maria Ordelaffi, who had started to court her.
This marriage would end the claims of the Ordelaffi family on the city of Forlì.
Antonio Maria, feeling confident, has written to the Duke of Ferrara that the Countess has promised to marry him.
When Caterina sees how things stand, she imprisons those who had spread the false news.
These promises are addressed by the Senate in Venice, which summons Antonio Maria to Friuli, where he will remain confined for ten years.
Caterina has meanwhile fallen in love with Giacomo Feo, the brother of Tommasso Feo, the castellan who had remained faithful to her after the assassination of her husband.
Caterina marries him in 1488, but secretly, to avoid losing custody of her children and the regency of her dominions.
