Indeed she didn't plan to do that, aswell as she didn't planned to fix her mistakes, she saw taesoo is paying for every mistake she had made so far, and she was okay with that.
That's as bad as doing it on purpose. She created a problem, she gave it to Taesoo, and then she ran away from the blame, she didn't even helped him.
Well, if there's something we can thank her is that thanks to her taesoo got to meet Sooha.
You know what scares me about her the most? It's like what you said: she was a bitch after the honeymoon phase wore out. So what if that also happens with the manager? It's clear that she can become super cruel to her partner if things don't go her way. Now she and the manager are in their honeymoon phase, but the manager hasn't been with her for as long as Doh and Teaso were together. So there's a very real possibility that if she ends up marrying the manager, and they're together for a while, she could end up treating him the same way she treated Taeso and I honestly don't want the manager to have to deal with that.
...is trying to paint Ms. Doh as not a 100% vicious and manipulative person, she just has a bad attitude no proper way to deal with stress (plus she money hungry and self-centered). The author is trying to say she didn't plan/lie the entire thing that got Moon Taeso fired, however, she was a bitch after the honeymoon phase wore out as she had to take care of him. but all in all, because she cares little but for her own good, she is still a terrible person.
I just want the truth to come out and for Taeso's character/reputation to be redeemed.