It was also custom that women did not have any legal rights or voices. It never entered the minds of these generations that a woman could become a legal guardian for a child, that could become a valuable pawn in the making and breaking of alliances.
A notable exception was Sisi's sister Helene, who got customary over her children after her husband's death. Her father in law clearly saw the potential in her and trusted her. He seemed to have been more open minded than other men of his generation.
Indeed, in the end she got the best marriage of all the in Bavaria sisters. Sadly, it was only short lived as her husband passed away early.
Also some heart break about her children.