The Light Novel series is the source material for the adaptation of the Anime and Manga series. The information and terminology on the article will be based on the source material rather than the adaptions.
During their time at the Royal Academy, Gabriele fell deeply in love with the son of the fourth Aub Ehrenfest. Due to her having a rather small mana capacity for an archduke candidate of a greater duchy her prospects of marrying into an archducal family were low, but since at the time Ehrenfest was just a minor duchy with a much lower average in mana capacity among it's nobles, this was not an issue in this case. She used her position as the daughter of a greater duchy's archduke to force the marriage through, disregarding what her future husband or his family might wish.
At the time the marriage happened, her husband was already married to a noblewoman of Liesegang. That woman was demoted to second wife, with Gabriele becoming the new first wife. Fearing the political dissent resulted from demoting the noblewoman from Liesegang (the most powerful faction back then) and increased influence of Ahrensbach, her husband was given a piece of land and appointed as Count Groschel, removing them from the archducal family. Gabriele would later find the life in such a backwater to be undesireable and longed to go back to her former home.
Gabriele deeply loved for her husband, but the newly minted Count Groschel did not reciprocate those feelings, since he was equally deeply in love with his former first, now second wife. Their marriage remained solely businesslike throughout their entire time together.
She encouraged the retainers that had come with her from Ahrensbach to marry into Ehrenfest families, but since essentially all archnobles had at least tenuous blood-ties to the Leisegang family, they chose to marry mednobles with particularly high mana capacity. This was the brith of what would later become the Veronica faction.
Gabriele gave birth to three children, two boys and one girl. Her firstborn son became a candidate to succeed Count Groschel due to his mana capacity and support from Ahrensbach, but he died too early to succeed the position. Her second child was Veronica, who would go on to marry the sixth Aub Ehrenfest and give birth to Georgine, Constanze and Sylvester.
During her final pregnancy, Gabriele fell ill and ultimately died soon after child labour, though her second son Bezewanst survived the ordeal. However his mana capacity was far below what was expected of an archnoble and thus he was sent to the temple to later become the High Bishop.
Her daughter Veronica was eventually married to Aub Ehrenfest and inherited the leadership of the faction Gabriele had built.