I think it was her idea though
Yes, it's quite possible considering the fact that she also wants to kills Zena. It might be a plan to trap Zena as well as killing Aristia (and so punishing the prince at the same time). But I really hope she is not stupid to orchestrate this herself.
I agree, she also said something about how the tea tasted, or smelled, stronger like in the first timeline. So maybe Jieun wasn't as simple and innocent as she seemed in the beginning. And maybe Tia's miscarriage was not an accident.
Oh my they really did this. Tell me Jieun couldn't be stupid enough to poison her? That would be such a dumb move considering this never happened before until she came in this world. Of course, people would be suspicious of her... at least, if they are not stupid enough.
But well, I'm almost sure this is the sh*tty Zena. He could have been too inpatient since she now can hear God's blessings (so obviously has the same power that Priest). #－.－)