In other timelines he was the worthless prince. The worst person to be allied with, Hence why he couldn't save her. And on top of it from the same spoilers you have read it seems she tried to help the "old" imperial family, but it backfired and got the "traitor" treatment from it. And since she is no Duke, archduke's daughter..... Her family being a count only family, that have little to no power at all. 

Reminder how it works

Count>Marquis>Duke>archduke>emperor

Now depending on the power of said family things can change. A count family of extremely good swordsman can have more political power than a Duke in name only.