@Arakuei One major difference is that in Hourglass I find Aria's brand of villainy to be much pettier; ie. mostly improving her station while sniping back at Mielle. Not to mention she has a more superior position since Mielle is...less smart and experienced.
In Shadow, Elena is playing a much more dangerous game. The Duke's cronies are a smart, ruthless bunch willing to kill if needed, and 1 wrong move making Leabric doubt her usefulness could end in Elena's swift death. Plus Elena's motivated by righteous revenge.