Fate.

It seems like it really wasn't destiny.

Empress Anne is left with the entire burden of facing the unexpected situation, alone, mostly clueless and with little to no options ahead.
The Emperor's death is being kept a secret, as per her order, which is actually a wise move. ChangMi dying without an heir would lead to uprisings and more death.

She can't impersonate him, despite being a shifter, due to the fact she is pregnant and that blocks her powers. She doesn't have ways to take much more time.
Qing actually had a plan, for an occurrence like that, but he didn't have the time to select a successor. Qing's child can't be appointed, since it's not born, there is no way to know whether its male, and most importantly, it was conceived in secret, by Qing's will.
He didn't want the baby to have a terrible life, like his own early life, or to be in danger. For that reason, he never met the Empress in an official way, as it usually happens in the Imperial Family. It was meant as a safety measure for both her and the baby in case he would have a sudden death. He was paranoid and expecting it could happen.

Anne is northern, though. She doesn't know enough of the Eastern aristocracy to come up with a name to fill the official edict Qing prepared to establish a successor and she knows it can't just be any random person.
What Qing wanted to assure was that a civil war wouldn't occur and she wants to fullfil his deepest wish.
The only person she fully trusts is Xoi and she asks him to come up with a list of potential candidates that would make a worthy successor, before they will be forced to reveal that Qing is dead.

She also doesn't plan to keep the baby with her, once it will be born, as a way to ensure it will never be linked to the Crown and risk to end up in the hands of powerthirsty people who'd use it to achieve their goals.