I read for the first time about her, years ago in the splendid work from John Julius Norwich: The Kingdom in the sun.
https://www.amazon.com/Kingdom-1130-1194-John-Julius-Norwich-ebook/dp/B07883SK8B

There for the first time I read about Constance, daugther of the famous Roger II of Sicily, 40 years old and pregnant. And as she was afraid that her baby, the future Frederick II Stupor Mundi, wouldn't be recognized as hers, she had her baby in a tent on the market place of a small town near Ancona and she invited the town matrons to witness the birth of her son. She even breast-fed her son publicly to support the veracity;

What a woman...a real daughter of her famous father...Roger II.

How came it all that far?

William II king of Sicily from 1166 to 1189 and married to Joan of England. Joan of England was the daugther of the English Henry II and another famous woman: Eleanora of Aquitaine. And as such she was Queen consort of Sicily.

Constance, as aunt of William II became in 1172 heir presumptive to the Sicilian crown. But I guess for "political" reasons she was kept in a convent as potential for the case if there were no other solutions.
And as William II was childless from Joan of England, Constance was freed from convent and betrothed in 1184 to Henry VI, son of Holy Roman Emperor Frederick Barbarossa.

William II, as he was afraid that the nobles of Sicily would be reluctant to welcome a German Hohenstaufen king, he let them promise to recognize Constance's succession. Nevertheless after his sudden dead in 1189 his cousin and Constance's nephew, Tancred seized power in Sicily. The widow Joan of England supported Constance, but was put under house arrest with confiscation of her estates. King Richard I of England, her brother wasn't pleased with that, to say no more.

When after the dead of Frederick Barbarossa, Henry and Constance were crowned Emperor and Empress, Constance and her husband went to Sicily to claim her rightly as queen of Sicily. The army succumbed to diseases on their way to Siclly. Even Henry became ill. At the end he had to retreat and let Constance with a small garrison behind in the wake of his return. There she was captured and delivered to Tancred, but nevertheless she behaved in all that turmoil and captivity as a proud empress and didn't give in to her cousin Tancred. A proud medieval woman...
Under the custody of Tancred's wife Sybilla, Constance hadn't a good life. Sybilla pushed her husband even to murder Constance, but Tancred daren't...

Henry VI negociated with Pope Celestine III, who by the way had his own political strategy. By, under the treat of excommunication, pressing Tancred to let her go to Rome, he thought to be able to avoid a uniting of the Holy Empire with Sicily. But when Constance was released in 1192 the clever imperial soldiers could free her and bring her over the Alps safely back to her husband.  

When Tancred suddenly died in 1194, Henry was already preparing to invade Sicily. He moved quickly to Palermo, deposed Tancred's son and was himself crowned.
And as Constance, pregnant, couldn't follow that quicky, she give birth, as mentioned in the beginning, to a son, the later named Stupor Mundi by the Roman Church as he was depicted as the anti-christ for political reasons with vile propaganda.

PS: And they lay all to rest in the cathedral of Palermo...
http://www.bestofsicily.com/mag/art417.htm
"The side chapel that is located near the portico entrance of the church is famous for its royal tombs. It is here that King Roger II is buried, along with his daughter, Constance de Hauteville, mother of Emperor Frederick II Hohenstaufen, who is also laid to rest here. Henry VI Hohenstaufen, Holy Roman Emperor, father of Frederick and husband of Constance, is also entombed here. Frederick II, who besides being the King of Sicily was the Emperor of the Germans, has not been forgotten by the modern-day descendants of his Teutonic subjects. Even though Frederick has been dead for more than seven centuries, don't be surprised if you see German tourists leaving flowers at the foot of the Emperor's tomb. Other personages, including Bishop Walter himself, are interred in the crypt."

PPS: and I was there some years ago.

Kind regards, Paul.