Guena was sharp and intelligent, a ruthless political machinator. When her father died, her young nephew Mikhail was the next-in-line to the throne; knowing that Mikhail's youth would lead to an unstable leadership, Guena quickly married Aurelian, so as to provide her father with an alternate heir better disposed to rule Varuz.
After becoming Duchess, Guena used her political influence to control Varuz in secret, forming both a professional and romantic attachment to Aurelian's advisor, Lord Bernhardt. The two of them worked in secret against Aurelian's wishes, whenever they felt that he was making poor decisions in his capacity as ruler. Most notably, they attempted to broker peace with Duke Conrad, despite Aurelian's urge to go to war.
Shortly after the Twelfth Doctor and Clara Oswald's arrival in Varuz, Aurelian discovered the truth of Guena and Bernhardt's affair. Enraged, he kept them separated for much of the remainder of his time as ruler. Guena was skeptical of Lancelot upon his arrival in Varuz, and after Aurelian sent his knights away to aid Lancelot with his quest, it was her who persuaded him to recall them.
When Aurelian was slain in combat against Conrad's armies, Bernhardt and the Doctor rescued Guena from Varuz before it was invaded by the enemy soldiers. The Doctor took both of them in the TARDIS to a remote corner of Conrad's lands, far away from Varuz, where they could live in peace and anonymity. Guena and Bernhardt spent many happy years together in their new life, before she eventually passed away. (PROSE: Royal Blood)