Yes, if you want to be reductive. However, my bigger issue is that the story did not build up to the wrongful termination nor would the MC's and ex's actions, besides the break up (and even then the ex was passive when her partner screwed over the MC), would lead to her being terminated. Thus the story made the owner do it because she disliked the ex which feels unsatisfying as the owner was a background character up until now.
Right. So, a few things:
This isn't Kaori's downfall/faceslapping, it's the beginning. More satsifying stuff happens later.
You seem to think Kaori shouldn't have been fired, and you're absolutely right. By all accounts, including the author, this is wrongful termination. She is a competent worker who the owner fired for personal reasons. Is that fair? Absolutely not. The owner even said so. It's not meant to be fair or logical.
Kaori didn't directly fire Reito and she wasn't involved with his blacklisting, but she cheated on him, and let her new BF fire Reito unjustly. If you sit there and watch as your SO breaks the law and don't try to stop them, you're an accomplice. She didn't pull the trigger, but she didn't try to stop it either.
While her only directly malicious action was cheating, and she didn't deserve to be fired over that. The story never once claimed "Kaori deserved to be fired for this." and in fact said the opposite with "even if you bring this to court and ruin the brand, I will never forgive you." It's entirely a personal action by the owner.