@privkz it's not just "power" it's her identity, she wouldn't know who she was without that role. It's been brought up before by the Lipt ambassador that her whole life was dedicated towards this role. She is the Empress but she's also nothing if not the Empress.
It's mostly an anxiety issue, aggravated by Sovieshit's behaviour. She feels insecure in more ways than one.
And it's not like she knows for sure that Heinry plans to invade her country, she just knows he's up to something.
Also also, she's not exactly selling herself. She's admitted she feels at ease with him, more than she is in her current relationship, and in this story marriages of convenience were the norm. You could say her family "sold" her as a child to become the Empress, so there's continuity there.