When I say build I don't mean she builds things. Jezera is the one who negotiates alliances, puts spy networks together, and so on and so forth. She's still ruthless, she's still a killer, she's still a petulant brat but she recognizes the need for more than just wanton violence and devastation. Jezera is the one who, once the dust settled from Rowan conquering the realms for them, would set about rebuilding the necessary infrastructure to rule. Jezera, when not showing herself as an easily offended child, is the one most likely to hatch a plan, put that plan into motion, and get the best result. She may not be hammering nails into boards, but without her there would be absolutely no framework for Andras to work in and he'd probably never ascend to anything more than the leader of a small territory of orcs that would eventually get routed out by a hero.I know this is just a meme post, but real talk though, the twins could have potentially won me over to their side if they weren't so capriciously over-the-top cruel. The current order is shit and needs to be replaced. And Jezera talked a good game early on about freedoms and meritocracy and such. But the only freedom they seem to care about is the freedom for them to do what ever they want and the only merit they seem to care about is what benefits you can offer them. And every time I start to think working for them might not be so bad they pull some unnecessary cruelty for the lols.
I would hesitate to call Jezera a builder. I think they are both destructive, Andras is just destructive in the most obvious ways. If this was a family Andras would be the physically abusive father and Jezera would be the emotionally abusive mother. Their abuses are very different but they both lead to broken children. Neither twin is interested in actual leadership, they just want to have the ability to do whatever they want, whenever they want, consequence free. It is pure entitlement plain and simple.
It is pointed out several times by denizens of the castle that while the twins are ostensibly in charge, Rowan is the one that really runs everything. Of course if a Twin shows up you must pay all respect and follow any orders. But if you need anything you go see Rowan not a twin. The twins are only interested in themselves. Sure you could try to phrase your request in a way to appeal to that twins interests and if they see some benefit or entertainment in it they may do something for you. But they are just as likely to punish you for wasting their time if you fail to interest them or turn it around on you just for cruelty's sake. Rowan on the other hand has a vested interest in making sure everything is running smoothly and everyone is more or less taken care of. The twins want the benefits and effectiveness of a well regulated organization, but they aren't willing to put in the work for it and they want to be exempt from it rules. They why they put Rowan in charge of almost everything, while at the same time holding absolute control over him.
It's not even necessarily their fault I imagine that all beings of chaos inherently have difficultly maintaining any type or order. It's likely that the reason they revere the might-makes-right structure is simply because it is the only type of order they are inherently able to maintain.