I wasn't 100% sure of whether I wanted my female Dunmer thief/assassin to be a vampire, so I saved the game while Harkon was transforming.

I accepted to gift just to see what she would look like. After playing around a bit, I decided I rather have her join the Dawnguard anyhow.

When I loaded the save file Harkon did transform but that burst animation didn't happen, so he was stuck in a slouching stance.

The dialogue where he asks you to make your choice came up, but nothing happened after I refused his gift. Harkon says "I'll banish you" but just stays there, floating and doing nothing.

I can't believe I'm gonna lose my lvl 28 character because of something like this. Is there no way around it?

Don't you have any previous saves?

No, I don't do that.

EDIT: I can't even think clearly in the state I am. I thought it could be possible to change sides in the beginning just like the civil war. Got her cured, and saved it... over the save file I mentioned.

So much effort and time going to waste. I spent most of yesterday playing as her. And as someone who's been playing the game for so long, I do not have the strength to start this character over.

ahh this bug is familiar. had you taken a little time on this forum to read or search for posts of same nature, you'd found the answer easily.

Load a save prior to entering the castle. Once inside, move your character to an opposite side from Harkon of one of the tables in the great hall, then wait for him to initiate dialogue.