I do not think Nick threw her under the bus. He criticized her for faults that she clearly has.
Everyone on the show had to know that Isabelle was paying no attention to the time limits or to Tim. The idea that she would say "I thought that Tim meant there were ten more minutes (or whatever) until we had to leave the studio, not ten minutes until we had to be on the runway" was ludicrous, because he specifically went in there and told her what the time limit meant. She had to know. Her extra time spent working on her clothing gave her an unfair advantage over the other designers.
Whatever Isabelle's talents as a designer, this is not someone who should have been on a show where time management is an important element. Moreover, she all but told Nick to shut up when he advised her. At the very least she was clueless about how to work with other people, which is a skill she'll need if she wants to be in this industry. If she wants to become one of those home artisans who makes all her own clothes in solitude and sells them at street fairs and on Etsy, one by one, then her temperament is no problem, but if she wants to take part in any larger enterprise, she has to learn how to observe certain conventions of behavior. She can't always have her own way.
I have liked Zendaya since her stint on Dancing with the Stars. She seems like a hugely talented, well brought up, modest young person, and I hope she will have a long and varied career. She's so poised and articulate for her age, isn't she? And of course she's built like a model, with that tall, trim figure. Like Taylor Swift, she can become a darling of the fashion scene as well as an enjoyable performer.