Fists of the Wind

The Leveilleurs are the closest thing to a dynasty in Old Sharlayan--they have a long history of producing powerful mages, which Ameliance surely knew. Also, if the size of that mansion tells us anything, they are absolutely filthy rich.

While she speaks a bit self-effacingly of needing the servants' help to learn how to be a lady of the house, it is known that Ameliance also comes from a powerful and influential family, so I have my doubts that she came into the marriage as naive and unskilled as she pretends. Ameliance is adept at the social graces befitting a lady of the house, but she also seems to easily adopt a more friendly and personable manner (a skill her husband lacks). Her disarming sweetness and sense of humor put outsiders like the WoL at ease, win trust, make her appear candid and uncalculating. And it's quite possible she feels genuine affection for her cantankerous husband. That said look how organically she frames their courtship. She just happened to be captivated by the richest and most unapproachable boy in school! Naturally! It was fate, of course! And he was so flustered around her! Tee hee!

From what we see in Endwalker, she basically runs the household as well as its finances. Which, I will note, she is also disarmingly glib about. Oh, she just decided to finance the Scions because the household was packing up to go to space to escape the apocalypse anyway. Can't take it with you, you know! Certainly not because it served as opportunity to re-establish her family's influence outside the motherland after the loss of the colony, all while supporting her beloved children and the one organization with the potential to forestall said apocalypse!

Though she has also studied magic, Ameliance's real passion seems to be philanthropy, particularly in the realm of education. In Encyclopedia Eorzea v.3, it's mentioned that her family operated "private institutions of learning" in the Dravanian colony, which served as a healthy source of income. Those institutions would have closed their doors at the time of the exodus, the same year the twins were born. But the planning of the exodus began five years before that, after the Garlean invasion of Ala Mhigo. Ameliance's family might not have been ruined by this, but they would have seen the writing on the wall. Ameliance would have been around 19-20 at this time. Timeline details get fuzzy here, as we don't know precisely the typical age for Studium admission (only that the twins are atypical), or, I don't think, when Ameliance and Fourchenault were married. (Though since we've been told Elezen don't reach full physical maturity until 20+ I doubt they'd have been married before that, though you never know with rich people.)

My point is, I think you could make a case that Ameliance, the daughter of a wealthy family about to lose a significant source of their income, secured a strategic marriage to a similarly wealthy man whose family fortune was in no immediate danger of collapsing, and who was likely to spend most of his time wrapped up in his own work, leaving Ameliance maximum latitude to run the household, manage the finances, raise her children as she saw fit, and carry on her own family's legacy in supporting education at home and abroad.