I guess their idea was ''you can pick whatever dude you want for your secret marriage and we select a suitable empress'' then she kinda fucked it up by showing up with the empress candidate instead of the breeding stud.
Besides the whole secret marriage thing was a stupid idea in the first place, adoption would be politically safer bet. Like both the Emperor and Empress disappearing from public eyes for 9 months to cover up the pregnancy would be a pretty bad idea.
It is so politically poorly thought out...