Be bold. Propose!

Though you've only known her a short time, you've come to like Sonya extremely. Many a marriage between nobles is done with neither such knowledge of one another nor mutual liking, so it's not like this is a crazy move by the standards of your time. Even if the love in your relationship is not as strong as you think it is now, the match is still highly advantageous, which is what matters most anyways (at least in theory).

You catch one of the servants going by and ask them to bring Sonya to you to meet privately. The woman agrees, and runs off to tell Sonya the location. You wait in your hidden alcove anxiously, wondering if you should just stop this right now. The sudden arrival of the woman in question dashes these thoughts from your mind. "H-hello Sonya, I hope you are well" She laughs. "So formal. Is everything alright?" You're nervousness is reaching a fever pitch. "No, w-wait I mean yes, everything is ok. I just w-wanted to ask..." you breath deep, trying to clear the blockage from your throat. It's do or die. "Sonya, will you be my wife?" She looks at you in wide-eyed astonishment, unable to speak. In a moment though she regains control of herself. "Yes, yes I will!" she almost screams as she runs up and throws her arms around you, tears in her eyes. The relief and happiness you feel at the moment are immeasurable. The two of you stand there hugging and kissing for what feels like forever, though it could have been a few minutes, or an hour. In your bliss your comprehension of your surroundings is limited. All you care about is your sweet little fiance wrapped around you.

Being a grown woman, Sonya is fully in her right to marry you, whether her father is happy about it or not. Still, you'd like to avoid the bad blood of going behind a parent's back, especially when that parent is as irascible as Jan. Holding hands, you and Sonya look to one another for reassurance as you prepare to broach the topic to him. He is at his throne, waiting just behind the doors where you two are standing.