@akane12e
She didn't just come for a quick revenge, though. She came to make them suffer, too. And their threats are all bluffs, anyway. There's no one who looks like Veronica AND has the etiquette to play the daughter of a Duke, and her parents have escaped, so they have absolutely no leverage because if they kill her with the real Veronica gone, they have way more to lose. So Elena is actually the one with the advantage.
Aside from being a minor annoyance, the other things she's doing are for her benefit. If she didn't choose Hurelbad publicly, then Lea could just stage an accident and put Lorech up anyway. Getting rid of Veronica's furniture might have been the only unnecessary thing, but for her it's a trauma and she can get away with it, so why not? Acting stupid? If she acts too quiet or serious, then Lea will suspect her more. A commoner girl is supposed to be stupidly enchanted by the life of a noble. Literally almost everything she does is meant to throw them off guard/protect herself.
For what Elena went through, just ending the house isn't enough. She's there to bring misery, and that begins with exhausting the brains behind the plot, which is Lea. Her revenge began the moment Lea stepped into Elena's home.