They’re working on her next dress already:The designer did himself no favors with this dress.
He made a huge mistake in trying to size-up an existing design (which was not made with a woman Tess's size in mind) without modifying the design itself to be somewhat more flattering. He should have lowered the neckline--even a basic jewel neck would have been an improvement--so the dress wouldn't look like it's strangling her. And he (or at least whoever graded the pattern up to Tess's claimed size) probably didn't know how to draft a pattern for somebody that big in the first place, hence the too-small armholes and the poor fit over the bust.
Making clothes for fatties takes a certain skill set, one that most designers and patternmakers simply do not have, and I'm guessing this guy and his staff don't have it. I can see them thinking, "Well, it's not a very fitted dress, so maybe we can do it; why not?", only to realize too late they were in over their heads. And then, of course, Tess lies about her measurements.
If the designer had any name recognition at all, I could see him making her an ill-fitting, horribly unflattering dress as sabotage, had she been a pain in the ass. After all, nothing's going to look good on her. Christian Siriano had somebody whip up a leopard-print bag to cover her for one event, which was an obvious "fuck you," given the care he's put into garments for other plus-size celebrities (it didn't help that she was cavorting with his despised ex, and taking naked pics of herself with said ex and posting them to Insta, not long before the event). But this guy can't afford to do that; he's too new. So I suppose it's good for him that Tess can't afford to say shit about the dress, given how slim (tee hee) her options are these days when it comes to dressing for red carpet events.