Do you mean the render or the in-game model?
The render looks fine to me, but I agree the in-game model at the moment doesn't look right. Her face in particular is so blank and expressionless compared with the old look.
But it's possible the in-game model will be improved between now and the game's release. ZSS has barely shown up in any footage or screenshots of the game yet, which could be because they are still putting the finishing touches to the character model.
She is also one of the few characters who have not had any alternate costumes or colours shown off in screenshots or gameplay footage, which could also be be a sign they haven't finalised her look yet.
That's the optimistic view, but on the flipside it could be that they got some complaints about her in the last game, and have changed her design in Smash Ultimate in response to that.
But I guess nobody will know for sure until the game comes out in December or when they release more screenshots and gameplay footage closer to release.